Mdadm: Difference between revisions
From Leo's Notes
This page was last edited on 15 June 2023, at 17:02.
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== Quick Usage == | == Quick Usage == | ||
= | {| class="wikitable" | ||
{{highlight|lang=terminal|code= | !Task | ||
!Commands | |||
|- | |||
!Initialize disks | |||
|Initialize the disks in your array:{{highlight|lang=terminal|code= | |||
# mdadm --zero-superblock /dev/sdb | # mdadm --zero-superblock /dev/sdb | ||
# mdadm --zero-superblock /dev/sdc | # mdadm --zero-superblock /dev/sdc | ||
}} | }} | ||
|- | |||
!Creating a Raid 1 Mirror | |||
| | |||
{{highlight|lang=terminal|code= | {{highlight|lang=terminal|code= | ||
# mdadm --create /dev/md0 --chunk=4 --level=1 --raid-devices=2 /dev/sdb /dev/sdc | # mdadm --create /dev/md0 --chunk=4 --level=1 --raid-devices=2 /dev/sdb /dev/sdc | ||
}} | |||
|- | |||
!Creating a Raid 5 | |||
|{{highlight|lang=terminal|code= | |||
# mdadm --create /dev/md0 --chunk=128 --level=5 --raid-devices=4 /dev/sdb /dev/sdc /dev/sdd /dev/sde | |||
}} | }} | ||
You can specify hot spares with {{code|1=--spare-devices=N /dev/sdn}} | |||
|- | |||
To save your settings, run | !Saving mdadm config | ||
|To save your settings, run the following. Note that Ubuntu may have the file under <code>/etc/mdadm/mdadm.conf</code>.{{highlight | |||
{{highlight|lang=terminal|code= | | lang = terminal | ||
| code = # mdadm --detail --scan >> /etc/mdadm.conf | |||
# mdadm --detail --scan >> /etc/mdadm.conf | |||
# cat /etc/mdadm.conf | # cat /etc/mdadm.conf | ||
ARRAY /dev/md/0 metadata=1.2 name=data:0 UUID=5f486d36:37899fcb:99ad8485:088bc180 | ARRAY /dev/md/0 metadata=1.2 name=data:0 UUID=5f486d36:37899fcb:99ad8485:088bc180 | ||
}}The config will also need to be updated in the initrd file. Rebuild the initrd filesystem with: | |||
{{Highlight | |||
| code = # update-initramfs -u | |||
| lang = terminal | |||
}} | }} | ||
|- | |||
!Disassemble / stop an array | |||
|{{highlight|lang=terminal|code= | |||
{{highlight|lang=terminal|code= | |||
# mdadm --stop /dev/md0 | # mdadm --stop /dev/md0 | ||
}} | }} | ||
|- | |||
!Reassemble an array | |||
{{highlight|lang=terminal|code= | |{{highlight|lang=terminal|code= | ||
# mdadm --assemble --scan | # mdadm --assemble --scan | ||
}} | }} | ||
| Line 47: | Line 51: | ||
# mdadm --assemble /dev/md0 /dev/sdb /dev/sdc | # mdadm --assemble /dev/md0 /dev/sdb /dev/sdc | ||
}} | }} | ||
|- | |||
!Recovering an Array | |||
If you want to recover data from an array of a failed system, image the hard drives in case something goes terribly wrong. Then, attempt to reassemble the array with the {{code|-o}} or {{code|--readonly}} option for read only. This will prevent mdadm from attempting to resync, recover, or reshape the array. | |If you want to recover data from an array of a failed system, image the hard drives in case something goes terribly wrong. Then, attempt to reassemble the array with the {{code|-o}} or {{code|--readonly}} option for read only. This will prevent mdadm from attempting to resync, recover, or reshape the array.{{highlight|lang=terminal|code= | ||
{{highlight|lang=terminal|code= | |||
# mdadm --readonly --verbose --assemble /dev/md0 /dev/sdb /dev/sdc | # mdadm --readonly --verbose --assemble /dev/md0 /dev/sdb /dev/sdc | ||
# or | ## or | ||
# mdadm --readonly --verbose --assemble --scan | # mdadm --readonly --verbose --assemble --scan | ||
}} | }} | ||
{{highlight|lang=terminal|code= | |- | ||
!Check on the array status: | |||
|{{highlight|lang=terminal|code= | |||
# cat /proc/mdstat | # cat /proc/mdstat | ||
}} | }} | ||
|} | |||
== Issues == | == Issues == | ||
| Line 113: | Line 116: | ||
[[Category:Linux]] | {{Navbox Linux}}[[Category:Linux]] | ||
[[Category:LinuxUtilities]] | [[Category:LinuxUtilities]] | ||
Latest revision as of 17:02, 15 June 2023
mdadm is a Linux utility to manage software RAID.
Quick Usage
| Task | Commands |
|---|---|
| Initialize disks | Initialize the disks in your array:# mdadm --zero-superblock /dev/sdb
# mdadm --zero-superblock /dev/sdc
|
| Creating a Raid 1 Mirror |
# mdadm --create /dev/md0 --chunk=4 --level=1 --raid-devices=2 /dev/sdb /dev/sdc
|
| Creating a Raid 5 | # mdadm --create /dev/md0 --chunk=128 --level=5 --raid-devices=4 /dev/sdb /dev/sdc /dev/sdd /dev/sde
You can specify hot spares with |
| Saving mdadm config | To save your settings, run the following. Note that Ubuntu may have the file under /etc/mdadm/mdadm.conf.# mdadm --detail --scan >> /etc/mdadm.conf
# cat /etc/mdadm.conf
ARRAY /dev/md/0 metadata=1.2 name=data:0 UUID=5f486d36:37899fcb:99ad8485:088bc180
# update-initramfs -u
|
| Disassemble / stop an array | # mdadm --stop /dev/md0
|
| Reassemble an array | # mdadm --assemble --scan
You can assemble an array with specific devices using: # mdadm --assemble /dev/md0 /dev/sdb /dev/sdc
|
| Recovering an Array | If you want to recover data from an array of a failed system, image the hard drives in case something goes terribly wrong. Then, attempt to reassemble the array with the -o or --readonly option for read only. This will prevent mdadm from attempting to resync, recover, or reshape the array.# mdadm --readonly --verbose --assemble /dev/md0 /dev/sdb /dev/sdc
## or
# mdadm --readonly --verbose --assemble --scan
|
| Check on the array status: | # cat /proc/mdstat
|
Issues
Device or resource busy
If you're unable to reassemble an array with this error:
# mdadm --assemble /dev/md0 /dev/sdb /dev/sdc
mdadm: cannot open device /dev/sdb: Device or resource busy
mdadm: /dev/sdb has no superblock - assembly aborted
You probably forgot to define your /etc/mdadm.conf settings before rebooting and mdadm probably tried to do something with one of your disks to create /dev/md127 (hence the reason the device is busy). To free /dev/sdb in the above example, just stop /dev/md127 by running:
# mdadm --stop /dev/md127
And then retry reassembling the array again.
/dev/sdx is apparently in use by the system
An unmounted disk that has just been repartitioned cannot be formatted:
root@velocity:~# mkfs.ext4 /dev/sdb1
mke2fs 1.43.3 (04-Sep-2016)
/dev/sdb1 is apparently in use by the system; will not make a filesystem here!
If the disk was part of a RAID, Linux might helpfully make a raid device out of the disk and call it /dev/md127.
root@velocity:~# ls -al /dev/md127
brw-rw----. 1 root disk 9, 127 Jan 1 12:12 /dev/md127
Stop it, then retry making the filesystem again.
root@velocity:~# mdadm -S /dev/md127
mdadm: stopped /dev/md127
root@velocity:~# mkfs.ext4 /dev/sdb1
mke2fs 1.43.3 (04-Sep-2016)
Creating filesystem with 488378390 4k blocks and 122101760 inodes
...