1.1. Installation
Just install mdadm package
apt-get install mdadm
1.2. Documentation
Take a look in your directory
/usr/share/doc/mdadm/
1.3. Creating partitions
I prefere to use RAID with partitions instead of disks. Therefore, before proceding, the partitions shall be created.
Use your prefered tools (e.g.: cfdisk) and set the partition type to “FD”).
1.4. Autodetecting array
In order to autodetect your array at boot time, the following things are necessary:
- autodetection support in the kernel
- persistent superblocks shall be used (during creating)
- partition types set to FD
The autodetenction is the only way to boot the system from RAID.
1.5. Creating an array
To create a mirror with 2 harddisks (/dev/hda1 and /dev/hdc1):
mdadm –create –verbose /dev/md0 –level=1 –raid-devices=2 /dev/hda1 /dev/hdc1
Note: Using “–create” will create superblocks. With “–build” the superblocks are not created.
1.6. Creating an array without all disks
This can be very helpfull when system or data shall be migrated from not RAID to RAID harddisk and you don’t have a temporary place to store all.
mdadm –create /dev/md0 –level=1 –raid-disks=2 missing /dev/hdc1
In this case, the system or data can be in /dev/hda1. Once the raid is working, the system or data can be copied to /dev/md0.
After that, /dev/hda1 can be added to the array with
mdadm –add /dev/md0 /dev/hda1
1.7. Viewing array status
Very easily, the array status can be monitored with
mdadm –detail /dev/md0
or if you prefere
cat /pro/mdstat
1.8. Setting device to faulty
In order to test your array, you can simulate a break setting one device to faulty:
mdadm –manage –set-faulty /dev/md0 /dev/hda1
1.9. Removing a device
When a device is broken, before removing it physically, it shall be removed from the array:
mdadm /dev/md0 -r /dev/hda1
1.10. Adding a device
When a broken device has been replaced, it shall be added to the array:
mdadm /dev/md0 -a /dev/sda1
1.11. Monitoring array
To monitor the array with a daemon:
dpkg-reconfigure mdadm
dirty way:
mdadm –monitor –mail=root@localhost –delay=1800 /dev/md0&
This will send a mail to root when something happen.
1.12. Assembling array
To assemble (syncronize) the array:
mdadm –assemble
Alternatively:
mdadm –assemble –force
1.13. Configuration file
The configuration file is
/etc/mdadm.conf
but if you use autodetection, it is not necessary.
1.14. Stopping array
This stops the array, releasing all resources:
mdadm -S /dev/md0
1.15. Destroying array
The array can’t be really destroyed, because there is not a command providing such a feature.
Alternativelly, it is possible to make it not anymore visible to the system. This can be done with the following step.
Removing superblocks
mdadm –zero-superblock /dev/xxx
where xxx is the device (e.g.: hda1, sda1, …).
Now, the array will not be anymore automatically detected.
Note: This is enough to make the array invisible to the system, but the data are anyway there! If you want to safe erase them, give a look here: http://www.planamente.ch/emidio/pages/linux_tools_description.php (Secure data deletion).
2. Software RAID with raidtools2
2.1. Introduction
This tool is depracated. Use mdadm instead.
