Replacing failed device in boot mirror

TrueNAS General
1

So I replaced a failed device in a boot mirror on my scale system and noticed something.

The boot process took a lot longer because it failed to initialise the swap space. So I looked at the pool status and I get

  pool: boot-pool                                                                                                                                                                                                   
 state: ONLINE                                                                                                                                                                                                      
  scan: scrub repaired 0B in 00:00:35 with 0 errors on Mon Apr 22 20:34:10 2024                                                                                                                                     
config:                                                                                                                                                                                                             
                                                                                                                                                                                                                    
        NAME        STATE     READ WRITE CKSUM                                                                                                                                                                      
        boot-pool   ONLINE       0     0     0                                                                                                                                                                      
          mirror-0  ONLINE       0     0     0                                                                                                                                                                      
            sdj     ONLINE       0     0     0                                                                                                                                                                      
            sdk3    ONLINE       0     0     0

Notice how the original drive has the partition number on it, the replaced drive doesn’t.

Running fdisk, the replaced drive doesn’t have any partitions, which I presume is why the swap failed to initialise. Is this a bug?

2

And how did you do that? Did you manually run zpool replace, by any chance?

1 Like
3

bit offtopic but why would you need a mirrored bootpool?
save your config from time to time and you can always replace the whole bootdisk without any issues

4

To be able to recover from an inconvenient boot device failure in 5 minutes instead of two hours; and to be able to recover with zero downtime from a more conveniently-timed boot device failure.

4 Likes
5

It is also on the recommendations - I’m just sorting out my kit for a first install - and the instructions say very clearly:

We do not recommend installing TrueNAS on a single disk or striped pool unless you have a good reason to do so.

And

users often boot TrueNAS systems from 2.5" SSDs and HDDs (often mirrored for added redundancy).

That’s why I’ve planned to do it.

6

I did! The GUI kept giving me an error about an empty device so that was the only way

7

Great if you’re always in the same place as your NAS and can afford any amount of downtime. Not great for minimising downtime and recovery time.

8

Good point on downtime, but it takes only 5 minutes to recover failed boot drive if you have config file at least for me. It’s just a simple reinstall + upload config. Ok, the physical replacement will take like another 5-10 minutes tops, nowhere near 2 hours.

9

Not a bug then. You have to use the GUI for these things to work seamlessly - or you can manually replicate what the GUI does.

The immediately available solution is to replace the less-than-normally-replaced disk via the GUI. Of course, this is contingent on the specifics of that error you mentioned…

10

Hmm okay, I’ll give that a try and see if it resolves the issue. Thanks :slight_smile:

11

yup that’s solved it. I had to detach the drive via the command line with zpool detach then was able to re-attach it via the GUI. The partitions now look correct

1 Like
12

Truenas does a lot more than just attaching a device to a pool when boot mirroring.

1 Like