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ZFS Replace Disk Process (keep old disk online)

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I'm on Unraid 6.12.10, every time I do a replace following the guide via the GUI, it seems like it totally brings the old disk offline. For example looks like:

 

```

        NAME                       STATE     READ WRITE CKSUM
        primary                    DEGRADED     0     0     0
          raidz1-0                 DEGRADED     0     0     0
            sdc1                   ONLINE       0     0     0
            sdg1                   ONLINE       0     0     0
            sdj1                   ONLINE       0     0     0
            replacing-3            DEGRADED     0     0     0
              1123165010249792881  UNAVAIL      0     0     0  was /dev/sdi1
              sdd1                 ONLINE       0     0     0

```

 

Is there any way to adjust it so that the replace doesn't UNAVAIL the previous disk, and can use it for the reslivering process? 

 

It seems like the partition that was on /dev/sdi is just gone now that its removed from the pool. 

 

# fdisk  -l /dev/sdi
Disk /dev/sdi: 16.37 TiB, 18000207937536 bytes, 35156656128 sectors
Disk model: WDC WD180EDGZ-11
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes

 

Wondering if there is any way to fix this. 

Solved by JorgeB

  • Community Expert

That's the way the GUI does the replacement, first wipes the old disk, I believe there was a good reason for that, but at the moment don't remember, give me a couple of days to see if I can remember.

  • Author

I was able to restore the partition table and the data was still there, but the resilver had already started/ZFS didn't reonline the disk (I think it needs a fill import/export).

 

It makes the resilver a bit more risky as it can't use the old disk to verify checksums. I think this caused a few errors to pop up for me (I ended with 1-5 read/checksum errors after the resilver, not sure if thats normal). 

  • Community Expert
17 minutes ago, foreseeable-concertina5279 said:

I think this caused a few errors to pop up for me

It's not normal to errors because of this, assuming the pool and remaining disks were in good working order.

  • Community Expert
  • Solution

So IIRC, the main reasons for doing it this way for now are two fold:

 

-to prevent a user assigning a replaced pool disk to another pool array before it's wiped

-in case you are replacing a failing drive, a replace could take much longer if the disk has slow/failing sectors, while it waits for timeout and retries

 

But I believe that are are plans in the future to offer both options, but it may take a while, for now, if you prefer, you can also do a manual replacement using the CLI and then re-import the pool once the replacement finishes

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