Replace volume1 by another volume?

[tdse13]

Now I have time to fix my system after a faulty btrfs Raid1 volume crashed. The volume is read only. Since the disks are new and already replaced my idea is to use one of the 2 disks of the crashed volume and create a new volume3. Once all data are moved II would delete the remaining disk of volume1 and build a new raid1 out of the new volume3. Volume2 is in use for VMs.

 

Is this plan feasible? Thank you.

[flyride]

You can convert a Basic Storage Pool to a RAID1 at any time by adding an appropriate disk.

 

Understand the difference between the Storage Pool (where the array redundancy is) and the Volume (the filesystem, which has some corruption which is resulting in a read-only state).

 

You are proposing to sacrifice your healthy array redundancy and create another Storage Pool and Volume.  This will work logically, but this may be an inappropriate risk depending upon the value of the data and whether you have another copy somewhere else.  As always, redundancy in the RAID array is not a BACKUP.  It's a method of ensuring that your data remains immediately and functionally available in the event of a disk media failure of some sort.

 

If it were my data, I would insist on a copy of the data somewhere else before I deliberately sacrificed array redundancy.

[tdse13]

I made a backup of most data. However, I would like to use the setup (users, vm's, apps, docker, etc.) as they are. Moving all shared folders to a new volume should then do it.

 

One more question: My production system died with the volume read-only problem. Now I am using a similar backup  system (918+ and raid5). When checking dmesg I find btrfs errros related to docker: BTRFS error (device dm-1): cannot find qgroup item, qgroupid=2419 ! I don't want to get a second read only system. Do you have any idea what causes the errors and how to fix it? Thank you.

[tdse13]

@flyride

I do not use a basic volume but Raid1. I formated one of the 2 disks and started again. Unfortunately, I cannot move shares from the read-only remaining disk from the degraded Raid1 volume1 to the new basic volume3 since it is read-only. Any idea how to fix it? Thank you.

[flyride]

14 hours ago, tdse13 said:

I do not use a basic volume but Raid1. I formated one of the 2 disks and started again. Unfortunately, I cannot move shares from the read-only remaining disk from the degraded Raid1 volume1 to the new basic volume3 since it is read-only. Any idea how to fix it? Thank you.

 

Moving shared folders from the control panel is a write operation.  So that cannot be done on a read-only filesystem.

 

btrfs attempts to fix itself in real-time.  If it cannot due to corruption, it will mount read-only or fail to mount at all without external input.  There is a filesystem check tool but it really isn't intended to return a filesystem to service if it has suffered unfixable corruption. The correct course of action is to COPY the files from the read-only filesystem, which you are supposedly doing.

 

17 hours ago, tdse13 said:

When checking dmesg I find btrfs errros related to docker: BTRFS error (device dm-1): cannot find qgroup item, qgroupid=2419 ! I don't want to get a second read only system

 

If Synology's implementation of docker is installed to a btrfs filesystem, it will use btrfs snapshots in support of docker functionality.  Those snapshots can get corrupted on their own.  My experience is that again, the corruption cannot be fixed, but simply deleting and recreating the affected container will resolve the problem.

Edited October 19, 2021 by flyride