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I'm in the process of switching from a classic mdadm raid to a zfs pool, and have made a few stumbles that I'm trying to recover from.

Originally I had two 4tb drives in a raid 1 mirror.

I then put two new 4tb drives in the machine and disconnected the originals. I create a zpool with the new drives in a mirror, but I used /dev/sda, and /dev/sdb because that's what the guide I was using told me to do, and wasn't thinking.

So of course when I reconnected the old drives to copy the data over, they took /dev/sdb and /dev/sdc which made one of my two zfs drives /dev/sdd which of course messed up the zfs pool and showed one as UNAVAIL

After working with someone online I managed to get the zfs pool into UUID mode by zpool export pool and then zpool import -d /dev/disk/by-uuid pool

This then allowed me to detach the UNAVAIL drive, which I then wiped clean, and added back to the zfs as a mirror of the first using it's /dev/disk/by-id. After a few days it resilvered successfully.

Now, I have a zpool with one device having a long integer as it's identifier, and another with a string along the lines of ata-WDC_WD.... I wanted to get them all on the same page, so I was planning to detach the first disk with the integer identifier, and re-add it using it's /dev/disk/by-id. However, attempted to detach gives me the error: cannot detach 13419994393693470939: only applicable to mirror and replacing vdevs.

Ok, so I tried to replace it with a different drive, and got this error: cannot open '13419994393693470939': name must begin with a letter

While the pool is working, I would like everything to be in a consistent state. I could use the old two drives to make a new pool and copy the data back over, then destroy the old pool and then add those drives to the new one (which then requires me renaming the pools which causes some interruptions in service in the meantime), but I would hoipe there is a way around this I just haven't found.

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Just rerun the process you used to re-identify the disks the first time:

  1. zpool export pool
  2. zpool import -d /dev/disk/by-id pool

This will unify the drives to the by-id format. You could use by-uuid instead if you prefer to have it be in that format.

The two errors you're getting are:

  • cannot detach: This detach is being refused because ZFS thinks there are no other valid replicas of the data. Are you sure you configured the pool in a a mirror correctly? It's also possible the CLI is misinterpreting the error and giving you a nonsensical error message; maybe you're actually just running the command with the wrong name for the drive by accident (see next point below).
  • cannot open: I can't quite tell from the information you've given, but I suspect you need to give the full path to this device instead of just its UUID.
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  • Excellent! I hadn't realized I could use the -d option to specify the by-id. I have been mostly going by guides and posts and following the commands without understanding them. That's got them mapped correctly I think. As for the other points, running zpool status shows pool -> mirror-0 -> Drive1,Drive2. All with a state of ONLINE. And since it just resilvered, I assume the mirror is on correctly. But I suspect both the detach and replace were erroring because I was using just the UUID rather than the full path as you suggested. – sharf Dec 29 '18 at 5:51
  • Cool. That seems right to me. – Dan Dec 29 '18 at 18:20

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