ZFS - Remove a Disk from Pool

I currently have a ZFS pool with 16 disks. This pool is a temporary one and no data is currently sitting on the pool. A current migration requires a new disk and I do not have a spare with me at the moment.

Let's remove a disk from the current pool. Run it as degraded for the time being. I can bring a spare with me tomorrow and replaced the removed disk.

1) Pool and Disk information

Let's start listing our pools.

zpool list
NAME         SIZE  ALLOC   FREE  CKPOINT  EXPANDSZ   FRAG    CAP  DEDUP    HEALTH  ALTROOT
rpool        278G  21.9G   256G        -         -     8%     7%  1.00x    ONLINE  -
temp1-pool  8.72T  3.12G  8.72T        -         -     0%     0%  1.00x    ONLINE  -

We also need to know which disks are part of the pool.

zpool status -P temp1-pool
pool: temp1-pool
 state: ONLINE
  scan: scrub repaired 0B in 0 days 00:00:01 with 0 errors on Sun Jul 10 00:24:03 2022
config:

        NAME           STATE     READ WRITE CKSUM
        temp1-pool     ONLINE       0     0     0
          raidz2-0     ONLINE       0     0     0
            /dev/sdh1  ONLINE       0     0     0
            /dev/sdi1  ONLINE       0     0     0
            /dev/sdj1  ONLINE       0     0     0
            /dev/sdk1  ONLINE       0     0     0
            /dev/sdc1  ONLINE       0     0     0
            /dev/sdb1  ONLINE       0     0     0
            /dev/sdt1  ONLINE       0     0     0
            /dev/sds1  ONLINE       0     0     0
          raidz2-1     ONLINE       0     0     0
            /dev/sdu1  ONLINE       0     0     0
            /dev/sdr1  ONLINE       0     0     0
            /dev/sdq1  ONLINE       0     0     0
            /dev/sdv1  ONLINE       0     0     0
            /dev/sdp1  ONLINE       0     0     0
            /dev/sdw1  ONLINE       0     0     0
            /dev/sdo1  ONLINE       0     0     0
            /dev/sdn1  ONLINE       0     0     0

errors: No known data errors

I guess that /dev/sdn is disk in the slot 24 of my server.

{
        "slot-number": 23,
        "enclosure-id": "17",
        "enc-position": "1",
        "device-id": "37",
        "wwn": "5000C5007228FFB0",
        "media-error-count": "0",
        "other-error-count": "2",
        "predict-fail-count": "0",
        "pd-type": "SAS",
        "raw-size": 600126116593.664,
        "sector-size": "512",
        "logical-size": "512",
        "firmware-state": "JBOD",
        "serial": "SEAGATEST600MM00060004S0M2BLYE",
        "device-speed": "6.0Gb/s",
        "link-speed": "6.0Gb/s",
        "drive-temp": "29C",
        "os-path": "/dev/sdn"
      }

Perfect. The disk to be removed is /dev/sdn currently in slot 24. Well, actually slot 23 because the counting starts from 0.

2) Removing the Disk from the Pool

Since we now know the disk to be removed let's being.

We will use the command zpool offline.

zpool offline - takes the specified physical device offline. While the device is offline, no attempt is made to read or write to the device.

zpool offline temp1-pool /dev/sdn

There won't be any output when the command is launched. However, we can check if the disk is offline inspecting the pool.

zpool status -P temp1-pool
pool: temp1-pool
 state: DEGRADED
status: One or more devices has been taken offline by the administrator.
        Sufficient replicas exist for the pool to continue functioning in a
        degraded state.
action: Online the device using 'zpool online' or replace the device with
        'zpool replace'.
  scan: scrub repaired 0B in 0 days 00:00:01 with 0 errors on Sun Jul 10 00:24:03 2022
config:

        NAME           STATE     READ WRITE CKSUM
        temp1-pool     DEGRADED     0     0     0
          raidz2-0     ONLINE       0     0     0
            /dev/sdh1  ONLINE       0     0     0
            /dev/sdi1  ONLINE       0     0     0
            /dev/sdj1  ONLINE       0     0     0
            /dev/sdk1  ONLINE       0     0     0
            /dev/sdc1  ONLINE       0     0     0
            /dev/sdb1  ONLINE       0     0     0
            /dev/sdt1  ONLINE       0     0     0
            /dev/sds1  ONLINE       0     0     0
          raidz2-1     DEGRADED     0     0     0
            /dev/sdu1  ONLINE       0     0     0
            /dev/sdr1  ONLINE       0     0     0
            /dev/sdq1  ONLINE       0     0     0
            /dev/sdv1  ONLINE       0     0     0
            /dev/sdp1  ONLINE       0     0     0
            /dev/sdw1  ONLINE       0     0     0
            /dev/sdo1  ONLINE       0     0     0
            /dev/sdn1  OFFLINE      0     0     0

errors: No known data errors

3) Marking the Disk for Removal

My disks are configured as JBOD and connected using a megaRAID card. Because the disk is not part of an array. We do not need to mark it as offline, missing and prepare the removal.

Let's put its LED to blink and go the server to physically remove it.

megacli -PdLocate -start -physdrv[17:23] -a0
Adapter: 0: Device at EnclId-17 SlotId-23  -- PD Locate Start Command was successfully sent to Firmware 

Exit Code: 0x00

Conclusion

With the above steps we succesfully removed a disk from a ZFS pool.

Resources

5 Steps to Safely Replace a Drive in a Linux ZFS Array
How to safely replace a hard drive in a Linux ZFS Raid Array.
zpool-offline.8 — OpenZFS documentation

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