SkyWang Weekly

8. iperf3测速

Wed, 12 Mar 2025 00:00:00 GMT

Using iperf3 to test connection speed between different hosts.

Install iperf3

# CentOS
yum -y install iperf3
dnf install iperf3
# Ubuntu
apt-get -y install iperf3
# Alpine
apk add iperf3
# Arch Linux
pacman -S iperf3
# Windows iperf3 download links
# https://files.budman.pw/
# https://github.com/ar51an/iperf3-win-builds

iperf3 Speed Test Usage

iperf3 -s -p 5201

Where:

-s indicates server mode
-p specifies the port to use (default port 5201. Don’t forget to allow the port in the firewall)
-D runs as a daemon in the background, add the -D parameter

Then initiate the speed test from the local machine.

iperf3 -c 1.1.1.31 -p 5201 -t 30 -P 5 -R

Where:

-c indicates client mode and specifies the speed test server address
-p specifies the server port
-t specifies the test duration (in seconds)
-P specifies the number of concurrent connections (higher values help test speed limits)
-R is for reverse testing, indicating download speed test (without this parameter, upload speed is tested)
-u to test UDP connections, add the -u parameter
-i specifies the test interval in seconds

The [SUM] line contains the test data (based on the receiver), with an average bandwidth speed of 74.9 Mbits per second.

root@cloudcone-42:~# iperf3 -c 1.1.1.31 -p 5201 -i 1 -t 10 -P 5 -R
Connecting to host 1.1.1.31, port 5201
Reverse mode, remote host 1.1.1.31 is sending
[  5] local 64.69.40.42 port 55344 connected to 1.1.1.31 port 5201    # 5 threads started. The number in brackets at the beginning is the thread ID, mainly to distinguish each thread in the following data.
[  7] local 64.69.40.42 port 55356 connected to 1.1.1.31 port 5201    # All five threads successfully connected to the server, default port 5001
[  9] local 64.69.40.42 port 55366 connected to 1.1.1.31 port 5201
[ 11] local 64.69.40.42 port 55370 connected to 1.1.1.31 port 5201
[ 13] local 64.69.40.42 port 55378 connected to 1.1.1.31 port 5201
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-1.00   sec  15.8 MBytes   133 Mbits/sec   # First column, interval, indicates the time range
[  7]   0.00-1.00   sec  15.2 MBytes   128 Mbits/sec   # Second column, transfer, indicates the amount of data transferred
[  9]   0.00-1.00   sec  25.8 MBytes   216 Mbits/sec   # Third column, bandwidth, indicates the transmission bandwidth
[ 11]   0.00-1.00   sec  22.7 MBytes   190 Mbits/sec
[ 13]   0.00-1.00   sec  23.3 MBytes   196 Mbits/sec   # Since multiple threads are running simultaneously, the bandwidth of each thread is not the actual bandwidth
[SUM]   0.00-1.00   sec   103 MBytes   863 Mbits/sec   # The actual bandwidth is indicated by the SUM row. Our client command summarizes bandwidth reports every 1s, so adding the bandwidth of threads in the same time interval roughly equals the actual SUM bandwidth.
- - - - - - - - - - - - - - - - - - - - - - - - -
[  5]  29.00-30.00  sec  12.0 MBytes   101 Mbits/sec
[  7]  29.00-30.00  sec  17.6 MBytes   147 Mbits/sec
[  9]  29.00-30.00  sec  26.9 MBytes   226 Mbits/sec
[ 11]  29.00-30.00  sec  25.7 MBytes   215 Mbits/sec
[ 13]  29.00-30.00  sec  24.7 MBytes   207 Mbits/sec
[SUM]  29.00-30.00  sec   107 MBytes   896 Mbits/sec
...
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec   191 MBytes   160 Mbits/sec  968             sender
[  5]   0.00-10.00  sec   189 MBytes   158 Mbits/sec                  receiver
[  7]   0.00-10.00  sec   196 MBytes   165 Mbits/sec  873             sender
[  7]   0.00-10.00  sec   193 MBytes   162 Mbits/sec                  receiver
[  9]   0.00-10.00  sec   290 MBytes   244 Mbits/sec  1284             sender
[  9]   0.00-10.00  sec   287 MBytes   241 Mbits/sec                  receiver
[ 11]   0.00-10.00  sec   161 MBytes   135 Mbits/sec  744             sender
[ 11]   0.00-10.00  sec   160 MBytes   134 Mbits/sec                  receiver
[ 13]   0.00-10.00  sec   156 MBytes   131 Mbits/sec  724             sender
[ 13]   0.00-10.00  sec   155 MBytes   130 Mbits/sec                  receiver
[SUM]   0.00-10.00  sec   995 MBytes   835 Mbits/sec  4593             sender
[SUM]   0.00-10.00  sec   984 MBytes   826 Mbits/sec                  receiver
iperf Done.

Test Result Interpretation:

Concurrent Streams:

The test shows 5 concurrent streams (stream IDs 5, 7, 9, 11, 13), with the transmission details for each stream as follows:

[ 5]
Transfer: 18.7 MB (approx. 157 Mbps)
Send Rate: 160 Mbps
Receive Rate: 158 Mbps
Retransmissions: 968
...
[ 13]
Transfer: 17.0 MB (approx. 142 Mbps)
Send Rate: 131 Mbps
Receive Rate: 130 Mbps
Retransmissions: 724

Total Statistics:

Total Sent: 995 MB (approx. 835 Mbps)
Total Received: 984 MB (approx. 826 Mbps)
Total Retransmissions: 4593

Analysis:

Throughput: Through testing with 5 concurrent streams, the receiver received approximately 984 MB of data in total, and the sender sent approximately 995 MB. The overall throughput is roughly between 826 - 835 Mbps, indicating relatively stable network connection performance.

Retransmissions: The number of retransmissions (4593) indicates some packet loss occurred during transmission. While the packet loss is not extremely severe, the presence of retransmissions suggests the network is not completely error-free.

Speed Differences Between Streams: Stream 9’s transfer volume is significantly higher than other streams (252 Mbps), while streams 11 and 13 have lower rates (139 Mbps and 142 Mbps). This may indicate that network load balancing between different streams is not entirely uniform, or some streams are limited by network bottlenecks or other factors.

Summary:

The test results show that the average network connection speed over 10 seconds is approximately 835 Mbps (sent) and 826 Mbps (received), which is relatively ideal.

Although there are some retransmissions, there is no significant packet loss, and the variation in stream transmission rates suggests possible uneven network load or other factors affecting stream performance.

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7. ffmpeg 笔记

Tue, 17 Sep 2024 00:00:00 GMT

Merge All Videos in a Folder

find *.mp4 | sed 's:\ :\\\ :g'| sed 's/^/file /' > fl.txt
ffmpeg -f concat -i fl.txt -c copy output.mp4
// Ignore error messages
ffmpeg -safe 0 -f concat -i fl.txt -c copy output.mp4
rm fl.txt

Reference

Video Compression

// Video encoded with h.264, audio encoded with aac
ffmpeg -i input.mp4 -vcodec h264 -acodec aac output.mp4
// Video encoded with h.265, compressed to a smaller file
ffmpeg -i input.mp4 -vcodec libx265 -crf 28 output.mp4
// Video encoded with h.264, preserving better quality
ffmpeg -i input.mp4 -vcodec libx264 -crf 20 output.mp4

The smaller the crf, the higher the video quality; the larger the crf, the smaller the video file.

Encoding parameters can also be abbreviated, changing from -vcodec and -acodec to -c:v and -c:a:

1
2
3

ffmpeg -i input.mp4 -c:v libx264 -crf 23 output.mp4
ffmpeg -i input.mp4 -c:v libx265 -crf 28 output.mp4
ffmpeg -i input.mp4 -c:v libvpx-vp9 -crf 31 -b:v 0 output.mkv

Reference

Both AVC/H264 and HEVC/H265 are software encoders and are very slow. You can choose NVIDIA’s hardware encoders: hevc_nvenc and h264_nvenc, which use hardware acceleration and are very fast.

Reference

Using NVIDIA graphics card for encoding:

1	ffmpeg -i video.mp4 -c:v hevc_nvenc -crf 28 output.mp4

Transcoding a video from H.264 to H.265 took 55 minutes, reducing the video size from 3.8GB to 430MB, with immediate results. Transcoding command: ffmpeg -i 1.mp4 -c:v libx265 -vtag hvc1 -c:a copy 1_hevc.mp4

On Windows 10, you can install ffmpeg using scoop and update all programs installed via scoop on Windows with:
scoop list | foreach { scoop update $_.Name }.

Trim a video with the same encoding according to a specified time:

1	ffmpeg -ss 00:05 -to 08:53.500 -i ./input.mp4 -c copy video.mp4

Quickly edit a video using ffmpeg:

1	ffmpeg -ss 07:18 -to 13:45 -i ./aaa.mkv -c copy bbb.mkv

-ss indicates the start time
-to indicates the end time
-i is the input file
-c means using the same encoding as the original video
bbb is the name of the output file

Merge video and audio, keeping the video encoding unchanged and changing the audio encoding to aac:

1	ffmpeg -i 1.mp4 -i 1.opus -c:v copy -c:a aac output.mp4

Convert PNG format images to JPG format:

1	ffmpeg -i image.png -preset ultrafast image.jpg

Resize an image:

1 2	ffmpeg -i image.jpeg -vf scale=413:626 2-inch.jpeg ffmpeg -i image.jpeg -vf scale=390:567 1-inch.jpeg

Repeat an audio file 10 times:

1	ffmpeg -stream_loop 10 -i input.m4a -c copy output.m4a

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6. DELL服务器配置RAID

Tue, 23 May 2023 00:00:00 GMT

I. Requirement Description

The server has two 480GB SSD drives at the front and four 4TB HDDs at the back. The first two SSDs will be configured as RAID 1 for the operating system, while the four mechanical drives will be set up as RAID 5 for data storage.

II. Creating RAID 1 and RAID 5

2.1. After the server boots up, press F2 at the following screen to enter System Setup.

2.2. Inside System Setup, locate Device Settings.

2.3. Find Integrated RAID Controller1\:Dell\Configuration Utility. Select it and click to enter.

Note: The image above shows the server’s RAID controller card.

What does the H740P Mini RAID controller actually look like? See below:

The H740P Mini RAID controller primarily features an 8GB fast cache. This cache allows the RAID card to act as a buffer for read/write operations between server drives.

2.4. Then select Main Menu.

2.5. First, check if all drives are online and functioning properly. Select Physical Disk Management.

2.6. You can see that the two 480GB SSDs are in Ready status, and the four 4TB HDDs are also Ready. Return to the previous level.

2.7. Select Configuration Management.

2.8. Select Create Virtual Disk.

2.9. Under Select RAID Level, choose RAID 1.

2.10. RAID level is now set to RAID 1.

2.11. Next, select the first two SSD drives. Click Select Physical Disks.

2.12. Choose the two 480GB SSDs. Use the up/down arrow keys to highlight a drive and press the spacebar to check the box in front of it. After selecting both drives, click Apply Changes.

2.13. Click OK.

2.14. Configure RAID 1 parameters.

Virtual Disk Name: Name the RAID 1 virtual disk as needed.

Virtual Disk Size: Space size, select the default full capacity.

Virtual Disk Size Unit: Choose the unit for disk size.

Strip Element Size:

Stripe size, select the default 256KB. How to set the stripe size? For database server applications, typically choose 4-16KB. For large files, CAD, or rendering large images, it’s recommended to set it to 128KB or higher. For web servers or print servers, 16-64KB is sufficient.

Read Policy:

Choose Read Ahead mode: Pre-read mode. The advantage of this mode is that when a user reads data, the drive loads the data into the RAID card’s 8GB cache for delivery, rather than the user reading directly from the drive.

If you choose No Read Ahead mode: The user reads data directly from the drive, which is slower compared to Read Ahead.

Write Policy:

Choose Write Back mode: Write-back mode. When a user writes data to the drive, it is not written directly to the drive. Instead, the data is first written to the RAID card’s 8GB cache, and then the cache writes the data to the drive. This method is faster.

Write Through mode: The user writes data directly to the drive without using the RAID card’s cache. This mode is slower than Write Back.

Force Write Back mode: What does forced write-back mean? This relates to the RAID card’s battery. RAID cards are powered by batteries, which typically last about three years. Regardless of whether the RAID card has power, data is first written to the RAID card’s cache before being transferred to the drive. However, if the RAID battery dies after three years and data is being written to the server at that moment, the data in the cache could be lost in the event of a sudden power outage. It is not recommended to choose Force Write Back.

If Write Back mode is selected and the RAID card battery dies, the policy will automatically switch to Write Through mode.

Disk Cache: Select Default.

Default Initialization: Initialization, choose Fast for quick drive initialization. This allows you to install the operating system on RAID 1 immediately after creation without waiting. If you choose Full, you must wait for RAID 1 to complete initialization before installing the operating system. To check the initialization progress of RAID 1, refer to the end of this article.

2.15. Check Confirm, then click Yes.

2.16. Click OK.

2.17. After clicking OK, you will return to the previous screen. Continue creating RAID 5.

Under Select RAID Level, choose RAID 5.

2.18. After selecting RAID 5, choose Select Physical Disks.

2.19. Select the remaining four 4TB HDDs. Then click Apply Changes.

2.20. Click OK.

2.21. The parameters for RAID 5 are the same as for RAID 1. Then select Create Virtual Disk.

2.22. Check Confirm, then click Yes.

2.23. Click OK.

2.24. The drives have been created. Click Back. At this point, RAID 1 and RAID 5 have been successfully created.

III. Verification and Inspection

3.1. Check RAID Creation

Return to the Main Menu and find Configuration Management.

Select View Disk Group Properties.

Now, you can see two Disk Groups: one for RAID 1 and another for RAID 5. Both RAIDs have been created.

3.2. Check RAID Initialization Progress

Return to the Main Menu and find Virtual Disk Management.

Here, you can see that RAID 1 is initializing, currently at 12%.

Initialization at 16%. If you selected Full initialization for the RAID drives during parameter configuration, you must wait for RAID 1 to reach 100% initialization before installing the operating system.

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5. Linux命令总结

Mon, 12 Sep 2022 00:00:00 GMT

1. Basic Commands

uname -m Show machine processor architecture
uname -r Show kernel version in use
dmidecode -q Show hardware system components
(SMBIOS / DMI) hdparm -i /dev/hda List a disk's architecture characteristics
hdparm -tT /dev/sda Perform a test read operation on a disk
arch Show machine processor architecture
uname -m Show machine processor architecture
uname -r Show kernel version in use
dmidecode -q Show hardware system components - (SMBIOS / DMI)
hdparm -i /dev/hda List a disk's architecture characteristics
hdparm -tT /dev/sda Perform a test read operation on a disk
cat /proc/cpuinfo Display CPU info
cat /proc/interrupts Display interrupts
cat /proc/meminfo Verify memory usage
cat /proc/swaps Show which swap is being used
cat /proc/version Display kernel version
cat /proc/net/dev Display network adapters and statistics
cat /proc/mounts Display mounted filesystems
lspci -tv List PCI devices
lsusb -tv Display USB devices
date Display system date
cal 2007 Display 2007 calendar
date 041217002007.00 Set date and time - month day hour minute year.second
clock -w Save time modification to BIOS

2. Shutdown

shutdown -h now Shutdown system (1)
init 0 Shutdown system (2)
telinit 0 Shutdown system (3)
shutdown -h hours:minutes & Schedule system shutdown
shutdown -c Cancel scheduled system shutdown
shutdown -r now Reboot (1)
reboot Reboot (2)
logout Logout

3. Files and Directories

cd /home Enter '/home' directory
cd .. Go back one directory level
cd ../.. Go back two directory levels
cd Go to home directory
cd ~user1 Go to user1's home directory
cd - Go back to previous directory
pwd Show working directory
ls View files in directory
ls -F View files in directory
ls -l Show detailed list of files and directories
ls -a Show hidden files
ls *[0-9]* Show filenames and directory names containing numbers
tree Show tree structure of files and directories starting from root (1)
lstree Show tree structure of files and directories starting from root (2)
mkdir dir1 Create a directory named 'dir1'
mkdir dir1 dir2 Create two directories simultaneously
mkdir -p /tmp/dir1/dir2 Create a directory tree
rm -f file1 Delete a file named 'file1'
rmdir dir1 Delete a directory named 'dir1'
rm -rf dir1 Delete a directory named 'dir1' and its contents
rm -rf dir1 dir2 Delete two directories and their contents simultaneously
mv dir1 new_dir Rename/move a directory
cp file1 file2 Copy a file
cp dir/* . Copy all files in a directory to current working directory
cp -a /tmp/dir1 . Copy a directory to current working directory
cp -a dir1 dir2 Copy a directory
ln -s file1 lnk1 Create a symbolic link to a file or directory
ln file1 lnk1 Create a hard link to a file or directory
touch -t 0712250000 file1 Modify a file or directory's timestamp - (YYMMDDhhmm)
file file1 outputs the mime type of the file as text
iconv -l List known encodings
iconv -f fromEncoding -t toEncoding inputFile > outputFile creates a new from the given input file by assuming it is encoded in fromEncoding and converting it to toEncoding.
find . -maxdepth 1 -name *.jpg -print -exec convert "{}" -resize 80x60 "thumbs/{}" \; batch resize files in the current directory and send them to a thumbnails directory (requires convert from Imagemagick)

4. File Search

find / -name file1 Search for files and directories starting from '/' into root filesystem
find / -user user1 Search for files and directories belonging to user 'user1'
find /home/user1 -name \*.bin Search for files ending with '.bin' in directory '/home/user1'
find /usr/bin -type f -atime +100 Search for executable files not used in the last 100 days
find /usr/bin -type f -mtime -10 Search for files created or modified within the last 10 days
find / -name \*.rpm -exec chmod 755 '{}' \; Search for files ending with '.rpm' and define their permissions
find / -xdev -name \*.rpm Search for files ending with '.rpm', ignoring removable devices like CD-ROMs, flash drives
locate \*.ps Find files ending with '.ps' - run 'updatedb' command first
whereis halt Show location of a binary, source, or man page
which halt Show full path of a binary or executable file

5. Mount a Filesystem

mount /dev/hda2 /mnt/hda2 Mount a disk called hda2 - ensure directory '/mnt/hda2' exists
umount /dev/hda2 Unmount a disk called hda2 - exit from mount point '/mnt/hda2' first
fuser -km /mnt/hda2 Force unmount when device is busy
umount -n /mnt/hda2 Perform unmount operation without writing to /etc/mtab file - useful when filesystem is read-only or disk is full
mount /dev/fd0 /mnt/floppy Mount a floppy disk
mount /dev/cdrom /mnt/cdrom Mount a cdrom or dvdrom
mount /dev/hdc /mnt/cdrecorder Mount a cdrw or dvdrom
mount /dev/hdb /mnt/cdrecorder Mount a cdrw or dvdrom
mount -o loop file.iso /mnt/cdrom Mount a file or ISO image file
mount -t vfat /dev/hda5 /mnt/hda5 Mount a Windows FAT32 filesystem
mount /dev/sda1 /mnt/usbdisk Mount a usb flash drive or storage device
mount -t smbfs -o username=user,password=pass //WinClient/share /mnt/share Mount a windows network share

6. Disk Space

df -h Show list of mounted partitions
ls -lSr |more List files and directories sorted by size
du -sh dir1 Estimate disk space used by directory 'dir1'
du -sk * | sort -rn Show size of files and directories sorted by capacity
rpm -q -a --qf '%10{SIZE}t%{NAME}n' | sort -k1,1n Show space used by installed rpm packages sorted by size (fedora, redhat systems)
dpkg-query -W -f='${Installed-Size;10}t${Package}n' | sort -k1,1n Show space used by installed deb packages sorted by size (ubuntu, debian systems)

7. Users and Groups

groupadd group_name Create a new user group
groupdel group_name Delete a user group
groupmod -n new_group_name old_group_name Rename a user group
useradd -c "Name Surname " -g admin -d /home/user1 -s /bin/bash user1 Create a user belonging to "admin" group
useradd user1 Create a new user
userdel -r user1 Delete a user ( '-r' removes home directory)
usermod -c "User FTP" -g system -d /ftp/user1 -s /bin/nologin user1 Modify user attributes
passwd Change password
passwd user1 Change a user's password (root only)
chage -E 2005-12-31 user1 Set user password expiration date
pwck Check '/etc/passwd' file format, syntax, and existing users
grpck Check '/etc/passwd' file format, syntax, and existing groups
newgrp group_name Log into a new group to change default group for newly created files

8. File Permissions Use “+” to set permissions, use “-” to remove

ls -lh Show permissions
ls /tmp | pr -T5 -W$COLUMNS Divide terminal into 5 columns for display
chmod ugo+rwx directory1 Set read (r), write (w), and execute (x) permissions for owner (u), group (g), and others (o) on directory
chmod go-rwx directory1 Remove read, write, execute permissions for group (g) and others (o) on directory
chown user1 file1 Change ownership of a file
chown -R user1 directory1 Change ownership of a directory and all its contents
chgrp group1 file1 Change group of a file
chown user1:group1 file1 Change owner and group of a file
find / -perm -u+s List all files with SUID set in the system
chmod u+s /bin/file1 Set SUID bit on a binary file - user executing the file gets same permissions as owner
chmod u-s /bin/file1 Disable SUID bit on a binary file
chmod g+s /home/public Set SGID bit on a directory - similar to SUID, but for directories
chmod g-s /home/public Disable SGID bit on a directory
chmod o+t /home/public Set sticky bit on a file - only legitimate owner can delete the file
chmod o-t /home/public Disable sticky bit on a directory
chmod +x file_path Add execute permission for owner, group, and others
chmod -x file_path Remove execute permission for owner, group, and others
chmod u+x file_path Add execute permission for owner
chmod g+x file_path Add execute permission for group
chmod o+x file_path Add execute permission for others
chmod ug+x file_path Add execute permission for owner and group
chmod =wx file_path Add write and execute permissions for owner, group, and others; remove read permission
chmod ug=wx file_path Add write and execute permissions for owner and group; remove read permission

9. Special File Attributes Use “+” to set permissions, use “-” to remove

chattr +a file1 Allow file to be opened in append mode only for reading and writing
chattr +c file1 Allow kernel to automatically compress/decompress this file
chattr +d file1 dump program will ignore this file during filesystem backup
chattr +i file1 Make file immutable, cannot be deleted, modified, renamed, or linked
chattr +s file1 Allow file to be securely deleted
chattr +S file1 Make system immediately write modifications to disk after application writes to this file
chattr +u file1 If file is deleted, system allows you to recover it later
lsattr Show special attributes

10. Packing and Compressing Files

bunzip2 file1.bz2 Decompress a file called 'file1.bz2'
bzip2 file1 Compress a file called 'file1'
gunzip file1.gz Decompress a file called 'file1.gz'
gzip file1 Compress a file called 'file1'
gzip -9 file1 Maximum compression
rar a file1.rar test_file Create an archive called 'file1.rar'
rar a file1.rar file1 file2 dir1 Compress 'file1', 'file2' and directory 'dir1' simultaneously
rar x file1.rar Extract rar archive
unrar x file1.rar Extract rar archive
tar -cvf archive.tar file1 Create a non-compressed tarball
tar -cvf archive.tar file1 file2 dir1 Create an archive containing 'file1', 'file2', and 'dir1'
tar -tf archive.tar Show contents of an archive
tar -xvf archive.tar Extract an archive
tar -xvf archive.tar -C /tmp Extract archive to /tmp directory
tar -cvfj archive.tar.bz2 dir1 Create a bzip2 compressed archive
tar -xvfj archive.tar.bz2 Extract a bzip2 compressed archive
tar -cvfz archive.tar.gz dir1 Create a gzip compressed archive
tar -xvfz archive.tar.gz Extract a gzip compressed archive
zip file1.zip file1 Create a zip compressed archive
zip -r file1.zip file1 file2 dir1 Compress several files and directories into a zip archive
unzip file1.zip Extract a zip compressed archive

11. RPM Packages

rpm -ivh package.rpm Install an rpm package
rpm -ivh --nodeeps package.rpm Install an rpm package ignoring dependency warnings
rpm -U package.rpm Update an rpm package without changing its configuration files
rpm -F package.rpm Update an rpm package that is definitely installed
rpm -e package_name.rpm Remove an rpm package
rpm -qa Show all installed rpm packages in the system
rpm -qa | grep httpd Show all rpm packages containing "httpd" in their name
rpm -qi package_name Get specific information about an installed package
rpm -qg "System Environment/Daemons" Show rpm packages of a component
rpm -ql package_name Show file list provided by an installed rpm package
rpm -qc package_name Show configuration file list provided by an installed rpm package
rpm -q package_name --whatrequires Show dependency list for an rpm package
rpm -q package_name --whatprovides Show size occupied by an rpm package
rpm -q package_name --scripts Show scripts executed during installation/removal
rpm -q package_name --changelog Show modification history of an rpm package
rpm -qf /etc/httpd/conf/httpd.conf Confirm which rpm package provides the given file
rpm -qp package.rpm -l Show file list provided by an uninstalled rpm package
rpm --import /media/cdrom/RPM-GPG-KEY Import public key digital certificate
rpm --checksig package.rpm Verify integrity of an rpm package
rpm -qa gpg-pubkey Verify integrity of all installed rpm packages
rpm -V package_name Check file size, permissions, type, owner, group, MD5 check, and last modification time
rpm -Va Check all installed rpm packages in the system - use with caution
rpm -Vp package.rpm Verify an rpm package is not yet installed
rpm2cpio package.rpm | cpio --extract --make-directories *bin* Run executable files from an rpm package
rpm -ivh /usr/src/redhat/RPMS/`arch`/package.rpm Install a built package from an rpm source
rpmbuild --rebuild package_name.src.rpm Build an rpm package from an rpm source

12. YUM Package Updater

yum install package_name Download and install an rpm package
yum localinstall package_name.rpm Install an rpm package using your own software repositories to resolve all dependencies
yum update package_name.rpm Update all installed rpm packages in the current system
yum update package_name Update an rpm package
yum remove package_name Remove an rpm package
yum list List all installed packages in the current system
yum search package_name Search for software packages in rpm repositories
yum clean packages Clean rpm cache delete downloaded packages
yum clean headers Delete all header files
yum clean all Delete all cached packages and header files

13. deb Packages

dpkg -i package.deb Install/update a deb package
dpkg -r package_name Remove a deb package from the system
dpkg -l Show all installed deb packages in the system
dpkg -l | grep httpd Show all deb packages containing "httpd" in their name
dpkg -s package_name Get information about a specific package installed in the system
dpkg -L package_name Show file list provided by an installed deb package
dpkg --contents package.deb Show file list provided by an uninstalled package
dpkg -S /bin/ping Confirm which deb package provides the given file
APT Software Tools (Debian, Ubuntu and similar systems)
apt-get install package_name Install/update a deb package
apt-cdrom install package_name Install/update a deb package from CD
apt-get update Upgrade list of software packages
apt-get upgrade Upgrade all installed software
apt-get remove package_name Remove a deb package from the system
apt-get check Confirm dependency software repositories are correct
apt-get clean Clean cache from downloaded software packages
apt-cache search searched-package Return package names containing the search string

14. View File Contents

cat file1 View file contents from the first byte forward
tac file1 View a file in reverse starting from the last line
more file1 View contents of a long file
less file1 Similar to 'more' command, but allows reverse operations like forward operations in the file
head -2 file1 View first two lines of a file
tail -2 file1 View last two lines of a file
tail -f /var/log/messages Real-time view of content being added to a file

15. Text Processing

cat file1 file2 ... | command <> file1_in.txt_or_file1_out.txt general syntax for text manipulation using PIPE, STDIN and STDOUT
cat file1 | command( sed, grep, awk, grep, etc...) > result.txt Merge detailed description text of a file and write summary to a new file
cat file1 | command( sed, grep, awk, grep, etc...) >> result.txt Merge detailed description text of a file and write summary to an existing file
grep Aug /var/log/messages Find keyword "Aug" in file '/var/log/messages'
grep ^Aug /var/log/messages Find words starting with "Aug" in file '/var/log/messages'
grep [0-9] /var/log/messages Select all lines containing numbers in file '/var/log/messages'
grep Aug -R /var/log/* Search for string "Aug" in directory '/var/log' and subsequent directories
sed 's/stringa1/stringa2

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4. 配置PXE

Tue, 20 Jul 2021 00:00:00 GMT

PXE

Quick Start Guide. The following operations are performed on Ubuntu 20.04.

Install Required Software

apt install tftpd-hpa isc-dhcp-server nginx

Download Operating System ISO Images

rhel-server-7.9-x86_64-dvd.iso
rhel-8.3-x86_64-dvd.iso
Kylin-Server-10-SP1-Release-Build20-20210518-x86_64.iso
Kylin-Server-10-SP2-x86-Release-Build09-20210524.iso

Create a Local Repository

Using RHEL 7.9 as an example. The process is similar for other distributions.

mkdir -p /mnt/rhel79
mount rhel-server-7.9-x86_64-dvd.iso /mnt/rhel79
mkdir -p /var/www/html/rhel79/x86_64
cp -r /mnt/rhel79 /var/www/html/rhel79/x86_64/base

$ sudo vim /etc/nginx/sites-enabled/default
server {
  listen 80 default_server;
  root /var/www/html;
  autoindex on;
}

Create a Kickstart File

You can obtain this file from /root/anaconda-ks.cfg after manually installing the operating system.

mkdir /var/www/html/kickstart
cp rhel79.cfg /var/www/html/kickstart/

# The final directory structure is as follows:
/var/www/html
├── kickstart
│   ├── cdh.cfg
│   ├── gbase.cfg
│   ├── rhel79.cfg
│   ├── v10sp1.cfg
│   └── v10sp2.cfg
├── rhel79
│   └── x86_64
│       ├── addons
│       ├── base
│       └── updates
├── rhel83
│   └── x86_64
│       ├── addons
│       ├── base
│       └── updates
├── rhel84
│   └── x86_64
│       ├── addons
│       ├── base
│       └── updates
├── v10sp1
│   └── x86_64
│       ├── addons
│       ├── base
│       └── updates
└── v10sp2
    └── x86_64
        ├── addons
        ├── base
        └── updates

Configure DHCP

Note: First, configure the local machine’s IP address to 10.0.0.1.

$ sudo vim /etc/dhcp/dhcpd.conf
default-lease-time 600;
max-lease-time 7200;
log-facility local7;

option arch code 93 = unsigned integer 16;

subnet 10.0.0.0 netmask 255.255.255.0 {
  range 10.0.0.10 10.0.0.50;
  next-server 10.0.0.1;

  class "pxeclients" {
    match if substring (option vendor-class-identifier, 0, 9) = "PXEClient";

    if option arch = 00:07 or option arch = 00:09 {
      # x86-64 EFI BIOS
      filename "efi/x86_64/BOOTX64.EFI";
    } else if option arch = 00:0b {
      # ARM64 aarch64 EFI BIOS
      filename "efi/aarch64/BOOTAA64.EFI";
    } else {
      # Legacy non-EFI BIOS
      filename "bios/x86_64/pxelinux.0";
    }
  }
}

$ sudo vim /etc/rsyslog.d/dhcp-relay.conf
local7.* -/var/log/dhcp-relay.log

# Restart the service
systemctl restart isc-dhcp-server

Configure TFTP

$ sudo vim /etc/default/tftpd-hpa
TFTP_USERNAME="tftp"
TFTP_DIRECTORY="/srv/tftp"
TFTP_ADDRESS=":69"
TFTP_OPTIONS="--secure -vvv"

# Create BIOS directory
mkdir -p /srv/tftp/bios/x86_64

# Prepare pxelinux.0 and vesamenu.c32 files
cp /var/www/html/rhel79/x86_64/base/Packages/syslinux-4.05-15.el7.x86_64.rpm .
rpm2cpio syslinux-4.05-15.el7.x86_64.rpm | cpio -dimv
cp usr/share/syslinux/pxelinux.0 /srv/tftp/bios/x86_64/
cp usr/share/syslinux/vesamenu.c32 /srv/tftp/bios/x86_64/

# Prepare vmlinuz and initrd.img files
mkdir -p /srv/tftp/bios/x86_64/images/rhel79
cp /var/www/html/rhel79/x86_64/base/images/pxeboot/vmlinuz //srv/tftp/bios/x86_64/images/rhel79
cp /var/www/html/rhel79/x86_64/base/images/pxeboot/initrd.img /srv/tftp/bios/x86_64/images/rhel79

# Prepare the default file
mkdir /srv/tftp/bios/x86_64/pxelinux.cfg
cp /var/www/html/rhel79/x86_64/base/isolinux/isolinux.cfg /srv/tftp/bios/x86_64/pxelinux.cfg/default
$ sudo vim /srv/tftp/bios/x86_64/pxelinux.cfg/default
default vesamenu.c32
timeout 600

label local
  menu label Boot from ^local drive
  menu default
  localboot 0xffff

label rhel79
  menu label ^Install Red Hat Enterprise Linux 7.9
  kernel images/rhel79/vmlinuz
  append initrd=images/rhel79/initrd.img inst.ks=http://10.0.0.1/kickstart/rhel79.cfg quiet

label rhel83
  menu label ^Install Red Hat Enterprise Linux 8.3
  kernel images/rhel83/vmlinuz
  append initrd=images/rhel83/initrd.img inst.ks=http://10.0.0.1/kickstart/rhel83.cfg quiet

label v10sp1
  menu label ^Install Kylin Linux Advanced Server V10 SP1
  kernel images/v10sp1/vmlinuz
  append initrd=images/v10sp1/initrd.img inst.ks=http://10.0.0.1/kickstart/v10sp1.cfg quiet

label v10sp2
  menu label ^Install Kylin Linux Advanced Server V10 SP2
  kernel images/v10sp2/vmlinuz
  append initrd=images/v10sp2/initrd.img inst.ks=http://10.0.0.1/kickstart/v10sp2.cfg quiet

# Create UEFI directory
mkdir -p /srv/tftp/efi/x86_64

# Prepare BOOTX64.EFI, grubx64.efi, and grub.cfg files
cp /var/www/html/rhel79/x86_64/base/EFI/BOOT/BOOTX64.EFI /srv/tftp/efi/x86_64/
cp /var/www/html/rhel79/x86_64/base/EFI/BOOT/grubx64.efi /srv/tftp/efi/x86_64/
cp /var/www/html/rhel79/x86_64/base/EFI/BOOT/grub.cfg /srv/tftp/efi/x86_64/
chmod 644 /srv/tftp/efi/x86_64/BOOTX64.EFI
chmod 644 /srv/tftp/efi/x86_64/grubx64.efi

# Prepare vmlinuz and initrd.img files
mkdir -p /srv/tftp/efi/x86_64/images/rhel79
cp /var/www/html/rhel79/x86_64/base/images/pxeboot/vmlinuz /srv/tftp/efi/x86_64/images/rhel79/
cp /var/www/html/rhel79/x86_64/base/images/pxeboot/initrd.img /srv/tftp/efi/x86_64/images/rhel79/

# Prepare grub.cfg file
$ sudo vim /srv/tftp/efi/x86_64/grub.cfg
set timeout=5
set default=0

menuentry 'Install Red Hat Enterprise Linux 7.9' {
  linuxefi efi/x86_64/images/rhel79/vmlinuz ip=dhcp inst.ks=http://10.0.0.1/kickstart/rhel79.cfg
  initrdefi efi/x86_64/images/rhel79/initrd.img
}

menuentry 'Install Kylin Linux Advanced Server V10 SP1' {
  linuxefi efi/x86_64/images/v10sp1/vmlinuz ip=dhcp inst.ks=http://10.0.0.1/kickstart/v10sp1.cfg
  initrdefi efi/x86_64/images/v10sp1/initrd.img
}

menuentry 'Install Kylin Linux Advanced Server V10 SP2' {
  linuxefi efi/x86_64/images/v10sp2/vmlinuz ip=dhcp inst.ks=http://10.0.0.1/kickstart/v10sp2.cfg
  initrdefi efi/x86_64/images/v10sp2/initrd.img
  
# The final directory structure is as follows:
/srv/tftp
├── bios
│   └── x86_64
│       ├── images
│       │   ├── rhel79
│       │   │   ├── initrd.img
│       │   │   └── vmlinuz
│       │   ├── v10sp1
│       │   │   ├── initrd.img
│       │   │   └── vmlinuz
│       │   └── v10sp2
│       │       ├── initrd.img
│       │       └── vmlinuz
│       ├── pxelinux.0
│       ├── pxelinux.cfg
│       │   └── default
│       └── vesamenu.c32
└── efi
    └── x86_64
        ├── BOOTX64.EFI
        ├── grub.cfg
        ├── grubx64.efi
        └── images
            ├── rhel79
            │   ├── initrd.img
            │   └── vmlinuz
            ├── v10sp1
            │   ├── initrd.img
            │   └── vmlinuz
            └── v10sp2
                ├── initrd.img
                └── vmlinuz

View Logs

tail -f /var/log/syslog | grep dhcp
tail -f /var/log/syslog | grep tftp
tail -f /var/log/nginx/access.log

Debugging

# Test the repository
curl 10.0.0.1
curl 10.0.0.1/kickstart/rhel79.cfg

# Test DHCP
sudo nmap --script broadcast-dhcp-discover
sudo nmap --script broadcast-dhcp-discover -e eth0
dhcp-lease-list

# Test TFTP
$ tftp 10.0.0.1
tftp> get bios/x86_64/pxelinux.0
Received 27158 bytes in 0.1 seconds
tftp>

References

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3. Ubuntu安装Nvidia驱动

Tue, 13 Apr 2021 00:00:00 GMT

1. Preliminary Preparation

1.1 Check GPU Information

lspci | grep -i nvidia

1.2 Configure the Kernel

dnf install -y gcc dkms kernel-devel-$(uname -r) kernel-headers-$(uname -r)

The installed version must match the current kernel version.

1.3 Disable nouveau

# Check nouveau
lsmod | grep nouveau

# Disable nouveau
cat >  /etc/modprobe.d/blacklist.conf << EOF
blacklist nouveau
options nouveau modeset=0
EOF

1.4 Update initramfs

# AlmaLinux/RockyLinux
mv /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).img.bak
dracut /boot/initramfs-$(uname -r).img $(uname -r)

# Ubuntu
sudo update-initramfs -u

After completing this step, reboot the operating system before proceeding to the next step.

2. Install the Driver

2.1 Download the Driver

Download the driver for your corresponding graphics card from NVIDIA Driver Downloads. It is recommended to use the .run executable file. If you plan to install the CUDA Toolkit (which includes the driver), you can skip this step.

2.2 Install the Driver

bash NVIDIA-Linux-x86_64-470.256.02.run
or
bash NVIDIA-Linux-x86_64-470.256.02.run --kernel-source-path=/usr/src/kernels/$(uname -r) -k $(uname -r)

2.3 Verify Installation

nvidia-smi

If GPU-related information is returned, the installation was successful.

3. Install the CUDA Toolkit

3.1 Download the CUDA Installer

Visit CUDA and select the operating system and version that matches your GPU. Since the CUDA Toolkit includes the driver, you can skip Step 2 and proceed directly with the CUDA Toolkit installation. Driver versions corresponding to the CUDA Toolkit.

3.2 Install CUDA

bash cuda_11.4.0_470.256.02_linux.run

If the driver is already installed, be sure to deselect the driver installation option; otherwise, the installation may fail.

3.3 Verify Installation

/usr/local/cuda/bin/nvcc -V

If CUDA version information is returned, the installation was successful.

4. Install nvidia-fabricmanager

4.1 Add Software Repository

# AlmaLinux/RockyLinux
# Add the repository corresponding to your system version
dnf config-manager --add-repo http://developer.download.nvidia.com/compute/cuda/repos/rhel8/x86_64/cuda-rhel8.repo

# Ubuntu
# Add the repository corresponding to your system version
wget https://developer.download.nvidia.cn/compute/cuda/repos/ubuntu2004/x86_64/cuda-ubuntu2004.pin

mv cuda-ubuntu2004.pin /etc/apt/preferences.d/cuda-repository-pin-600

wget https://developer.download.nvidia.cn/compute/cuda/repos/ubuntu2004/x86_64/7fa2af80.pub

apt-key add 7fa2af80.pub

rm 7fa2af80.pub

echo "deb http://developer.download.nvidia.cn/compute/cuda/repos/ubuntu2004/x86_64 /" | tee /etc/apt/sources.list.d/cuda.list

4.2 Install nvidia-fabric-manager

# AlmaLinux/RockyLinux
dnf module enable -y nvidia-driver:470
dnf install -y nvidia-fabric-manager:470.256.02 nvidia-fabric-manager-devel-0:470.256.02

# Ubuntu
apt-get update
apt-get -y install nvidia-fabricmanager-470=470.256.02-1

4.3 Start the Service

systemctl start nvidia-fabricmanager
systemctl status nvidia-fabricmanager
systemctl enable nvidia-fabricmanager

4.4 Verify

nvidia-smi topo -m

If the returned results contain NV*, it indicates NVLink connections exist between GPUs. If all expected GPUs have NVLink connections and there are no error messages, then NVLink should be functioning normally.

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2. CentOS 7重置root密码

Mon, 03 Aug 2020 00:00:00 GMT

In a CentOS server, the permissions of a regular user are restricted by the root (super administrator). Sometimes, it’s inconvenient to download and install software in CentOS, so you need to access the root (super administrator) user interface. However, you might occasionally forget the root user’s password, requiring a reset. There are many versions of CentOS, but the method to reset the root user’s password is similar across them—entering single-user mode to modify the root password.

Detailed Steps to Reset the Root Password

Restart the server. When the system loading screen appears, press the e key on your keyboard to enter edit mode.
Move the cursor to find the line starting with linux16. Delete from the end until you reach ro and stop.

Change ro to rw, add a space, then append rd.break. Press Ctrl+X to boot.


Before modification: linux16 /vmlinuz-3.10.0-1160.e17.x86_64 root=/dev/mapper/centos-root ro crashkernel=auto rd.lvm.lv=centos/root rd.lvm.lv=centos/swap rhgb quiet LANG=en_US.UTF-8
After modification: linux16 /vmlinuz-3.10.0-1160.e17.x86_64 root=/dev/mapper/centos-root rw rd.break

Result as follows:

Enter single-user mode.

Enter the following commands to remount the root directory and reset the root password (e.g., to Aa@123456). Finally, reboot the system for the changes to take effect.

mount -o remount,rw /sysroot
chroot sysroot
echo 'Aa@123456' | passwd root --stdin
touch /.autorelabel     
exit
reboot

Process as follows:

After waiting for a while, when you return to the login interface, you can log in as root using the password you just set.

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1. 服务器RAID基本概念

Thu, 23 Jul 2020 00:00:00 GMT

Casually record some tech stuff, filtered and published here.

Basic Concepts of RAID

The full Chinese name of RAID is “独立磁盘冗余阵列” (Redundant Array of Independent Disks).

Redundant Array of Independent Disks (RAID), formerly known as Redundant Array of Inexpensive Disks, commonly referred to as a disk array. It uses virtualization storage technology to combine multiple hard drives into one or more disk array groups, aiming to improve performance, provide data redundancy, or both. During operation, depending on the RAID level, data is distributed across the drives in various patterns. RAID levels are named starting with “RAID” followed by a number, such as: RAID 0, RAID 1, RAID 5, RAID 6, RAID 7, RAID 01, RAID 10, RAID 50, RAID 60. Each level has its theoretical advantages and disadvantages, balancing between two goals: increasing data reliability and increasing storage (array) read/write performance.

In simple terms, RAID combines multiple hard drives into a single logical drive, so the operating system treats it as one physical drive. RAID is often used on server computers and typically uses identical drives for the array. Due to the continuous decline in hard drive prices and more effective integration of RAID functionality with motherboards, it has also become an option for ordinary users, especially for tasks requiring large storage capacity, such as video and audio production. ————Source: Wikipedia

Why Use RAID?

Using RAID primarily aims to achieve one or more of the following goals:

Improve Performance: Allow multiple hard drives to read/write data simultaneously, which is much faster than a single drive.
- It’s like having multiple workers move goods at the same time, much faster than one person.
Increase Fault Tolerance/Reliability: Through data redundancy (backup or parity), even if one drive suddenly fails, data is not lost, and service is not interrupted.
- It’s like making photocopy backups of important documents; even if the original is lost, the backup is still available.
Expand Capacity: Combine multiple small-capacity drives into one large logical volume for easier management and use.
- It’s like knocking down walls between small rooms to create one large hall.

** Important Note: RAID is NOT a substitute for regular backups! Its main purpose is to ensure service continuity and data availability. In cases of fire, accidental deletion, virus attacks, etc., data on RAID can still be lost. Therefore, you must adhere to the strategy of “RAID + Regular Backups.”**

Detailed Explanation of Hard Drive Requirements for RAID Levels

RAID 0 (Striping)

Minimum Drives: 2
Description: RAID 0 splits data into blocks and writes them alternately across all drives. It provides no redundancy or fault tolerance. If any single drive fails, all data is lost.
Advantages: Very high read/write performance (all drives work simultaneously).
Disadvantages: Lowest reliability. The more drives, the higher the overall failure rate.
Common Use Cases: Scenarios requiring extremely high performance where data is not critical or is temporary, such as graphics rendering cache, game storage drives.
RAID 1 (Mirroring)

Minimum Drives: 2
Description: RAID 1 writes complete data to every drive simultaneously, achieving 100% mirroring backup.
Advantages: Slightly improved read performance, write performance is the same as a single drive. High data security; as long as not all drives fail at once, data is not lost.
Disadvantages: Low disk space utilization (only 50%), high cost.
Common Use Cases: Scenarios requiring extremely high data security, such as operating system drives, log files for critical databases.
RAID 5 (Striping with Parity)

Minimum Drives: 3
Description: RAID 5 distributes data and parity information across all drives. It can tolerate the failure of any single drive. Usable capacity is (N-1) * single drive capacity.
Advantages: Excellent balance between capacity, performance, and security. Space utilization is higher than RAID 1.
Disadvantages: Poor write performance (requires parity calculation). After one drive fails, the array rebuild process is very stressful, time-consuming, and if another drive fails during this period, all data is lost.
Common Use Cases: Widely used in file sharing servers, small to medium-sized database storage, etc.
RAID 6 (Striping with Double Parity)

Minimum Drives: 4
Description: RAID 6 is similar to RAID 5 but uses two different parity algorithms, allowing it to tolerate the simultaneous failure of any two drives. Usable capacity is (N-2) * single drive capacity.
Advantages: Higher security than RAID 5, especially suitable for arrays with large-capacity drives (long rebuild times, double protection is safer).
Disadvantages: Write performance is worse than RAID 5 (requires calculating parity twice). Lower space utilization.
Common Use Cases: Arrays using large-capacity SATA drives, archival storage with extremely high data security requirements.
RAID 10 (Mirroring first, then Striping)

Minimum Drives: 4 (must be an even number)
Description: RAID 10 is a combination of RAID 1 and RAID 0. It first pairs drives into RAID 1 mirrored pairs, then combines these pairs into a RAID 0 striped volume.
Advantages: Combines the high security of RAID 1 with the high performance of RAID 0. Rebuild speed is much faster than RAID 5/6.
Disadvantages: Highest cost, disk space utilization is only 50%.
Common Use Cases: Scenarios requiring both high performance and high reliability, such as database servers, virtualization hosts, high-traffic websites.

Important Notes:

The above are minimum requirements. Except for RAID 1, other levels can use more than the minimum number of drives (e.g., RAID 5 can use 4, 5, 6… drives; RAID 10 can use 4, 6, 8… drives).
Hybrid RAID: There are other RAID levels (like RAID 50, RAID 60, etc.) that are combinations of the basic levels mentioned above and require more drives.
Hot Spare: In actual enterprise deployments, one or more hot spare drives are often configured. When a working drive in the array fails, the hot spare automatically replaces it and begins data reconstruction. This process requires no manual intervention, further improving system availability. Hot spares do not participate in daily RAID operations and are not counted in the minimum requirements above.

Common Scenario Examples: Which RAID to Use?

Operating System (OS) Drive and Critical Boot Drive
- Recommended: RAID 1
  - Reason: The OS drive typically doesn’t require huge capacity but has extremely high availability and reliability requirements. RAID 1 provides the best protection; if one drive fails, the system continues running seamlessly, making it easy to replace the drive and rebuild. Read performance is also improved, aiding system boot and operation.
File Storage Server / NAS
- Small/Medium-sized, Budget-sensitive: Recommended RAID 5
  - Reason: Achieves a perfect balance between capacity utilization and security. Offers the best cost-performance for servers storing general files like documents and images.
- Large-scale, using high-capacity drives (e.g., >4TB): Strongly recommended RAID 6
  - Reason: Rebuild times for high-capacity drives are very long (possibly over 24 hours), and the risk of a second drive failing during this period cannot be ignored. RAID 6’s double parity provides crucial safety.
Video Editing / Media Production
- Raw Footage Storage: Recommended RAID 5/6
  - RAID 5/6: A safer choice, providing sufficient bandwidth while ensuring data security.
- Finished Product Archiving: Recommended RAID 6
  - Data is important, large in volume, and needs long-term safe storage. RAID 6 is the best choice.

Important things need to be said three times: RAID is not backup! RAID is not backup! RAID is not backup! No matter how secure your RAID is, you must have a strategy for regular backups to other media (such as tape, offsite NAS, cloud storage).

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