Problems adding new disk to Raid 1

  • Hi,

    been using OMV for a few years (beginning of 2016) now and in the beginning added two 4TB drives in Raid 1. After a long time with no problems I now finally decided to buy a new 4TB drive to replace one of the old ones and keep that one as a backup.


    Now the problems start: My disks are somehow formated with a MBR. I can use the whole 4TB though. =O

    Everything I can find online says this is not really possible, although you could fiddle with the sectors and make it happen. Still: When trying to copy the MBR to write to the new drive it gives me an error.


    So...what to do now? Any ideas or topics to look for?

  • I'm not sure what that's all about regarding the MBR, or why you're trying to copy it to your new drive (?). My guess is that the RAID layer itself manages the entire 4TB capacity of your existing drives, independently of the MBR sector.


    In any case, my understanding is that you simply offline one of the two disks in the RAID, physically replace it with the new one (which should be completely blank, no prior formatting etc.) and let the RAID resync.


    Orrr... you could simply use the new drive to use for backups and leave the RAID be? (In which case, formatting the whole drive to ext4 should be a non-issue.)

  • Got it working today, the array is rebuilding as I write.


    Since I luckily never had to rebuild a RAID array I followed guides online. As you mentioned the RAID layer manages the file system, in the examples I found they used separate partitions. That's what threw me off.


    What I did:

    0. Boot off of an USB stick since there was some process running on OMV preventing me from properly managing the array, as it was always busy.

    1. Add the new drive to the RAID array as a spare (mdadm --manage /dev/mdXX -a /dev/sdx).

    2. Marking one of the other drives as needing replacement (mdadm --manage /dev/mdXX --replace /dev/sdy) marking it as failed would have worked as well.


    Orrr... you could simply use the new drive to use for backups and leave the RAID be? (In which case, formatting the whole drive to ext4 should be a non-issue.)

    Thought about doing this, although the idea was to replace one of the old drives so if/when one of them fails I have the chance the new one is fine. The third spare drive will be stored "offline", so worst case I have that one including the files up to the current date as another backup.

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