Change from raid5 to raid1

henfri · 3. Januar 2021

Hello,

I had my root-filesystem as raid5. Now I want to switch to raid1.

I have (had to) remove one drive already:

Code

/dev/md0:
           Version : 0.90
     Creation Time : Sat Sep 24 16:16:26 2016
        Raid Level : raid5
        Array Size : 62914432 (60.00 GiB 64.42 GB)
     Used Dev Size : 31457216 (30.00 GiB 32.21 GB)
      Raid Devices : 3
     Total Devices : 2
   Preferred Minor : 0
       Persistence : Superblock is persistent

       Update Time : Sun Jan  3 17:36:57 2021
             State : clean, degraded
    Active Devices : 2
   Working Devices : 2
    Failed Devices : 0
     Spare Devices : 0

            Layout : left-symmetric
        Chunk Size : 64K

Consistency Policy : resync

              UUID : 25f603ac:8a3750de:ded2cb5c:26b13161
            Events : 0.11968535

    Number   Major   Minor   RaidDevice State
       0       8       49        0      active sync   /dev/sdd1
       1       8       65        1      active sync   /dev/sde1
       -       0        0        2      removed

Alles anzeigen

Is it now possible to change from this degraded raid5 to a raid1?

I tried this:

Code

mdadm --grow -l 1 -n 2 /dev/md0
mdadm: Can only convert a 2-device array to RAID1
root@homeserver:/home/henfri# mdadm --grow  -n 2 /dev/md0
mdadm: this change will reduce the size of the array.
       use --grow --array-size first to truncate array.
       e.g. mdadm --grow /dev/md0 --array-size 31457216

But when I execute the suggested step, the system gives me an ext4 error.

Regards,

Hendrik

ryecoaaron · 4. Januar 2021

You ran your OS on raid 5?? Degraded raid 5 array is still twice the size as a raid 1. So, you need to shrink the filesystem before you can do that. You can't do that while the root filesystem is mounted read write.

henfri · 4. Januar 2021

Hello,

yes, that is what popped into my mind when lying in bed yesterday... Sorry.

So, I boot to systemrescuecd, then do a fsck, then a resize2fs.

Then, I do a mdadm --grow /dev/md0 --array-size 31457216 to shrink the array.

Then, with mdadm --grow -n 2 /dev/md0 I can reduce to two devices.

Finally, with mdadm --grow -l 1 /dev/md0 I can change to raid1

Correct?

Alternatively... I have a backup (fsarchiver).

I could wipe the array create a new one and restore into that.

What would you recommend?

The second option lets me (for the first time) check my recovery strategy... So I sympatize with it.

Regards,

Hendrik

ryecoaaron · 4. Januar 2021

Zitat von henfri

Correct?

Seems like it would work but I haven't shrunk many mdadm arrays (probably none).

Zitat von henfri

Alternatively... I have a backup (fsarchiver).
I could wipe the array create a new one and restore into that.

What would you recommend?

I would shrink the filesystem size and clone it with clonezilla. Then create a new array. Then you have a backup in case anything goes wrong.

henfri · 14. Februar 2021

It worked, thanks

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