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I had a 4-disk mdraid of 8.12TB with zfsonlinux's ZFS:

# zpool status
  pool: tank
 state: ONLINE
  scan: none requested

    NAME                  STATE     READ WRITE CKSUM
    tank                  ONLINE       0     0     0
      md-name-ubuntu:md2  ONLINE       0     0     0

To which I added two more disks:

# mdadm --add /dev/md2 /dev/sde /dev/sdf
# mdadm --grow /dev/md2 -n 6

This finished successfully:

# mdadm --detail /dev/md2
        Version : 1.2
  Creation Time : Thu Jan 16 01:53:23 2014
     Raid Level : raid5
     Array Size : 14597903360 (13921.65 GiB 14948.25 GB)
  Used Dev Size : 2919580672 (2784.33 GiB 2989.65 GB)
   Raid Devices : 6
  Total Devices : 6
    Persistence : Superblock is persistent

During resizing, the ZFS was unmounted but not exported. It still reports its old size:

# zpool list
tank  8.12T  7.78T   349G    95%  1.04x  ONLINE  -

Now I tried each of these steps to expand it, all of which somebody somewhere claimed would work:

# zpool set autoexpand=on
# zpool export tank
# zpool import tank

Did nothing.

# zpool export tank
# zpool import -o autoexpand=on tank

Did nothing.

# zpool export tank
# zpool import -o expand=on tank

Did nothing.

# zpool online -e tank md-name-ubuntu:md2

Did nothing. It's not a problem with the weird name either, I also tried

# zpool export tank
# zpool import -d /dev/ tank
# zpool online -e tank md2

Except, a few minutes later as I'm writing this post, the partition table seems to have been updated (no idea which of the commands I tried caused this)

# gdisk -l /dev/md2
Found valid GPT with protective MBR; using GPT.
Disk /dev/md2: 29195806720 sectors, 13.6 TiB

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048     29195788287   13.6 TiB    BF01  zfs
   9     29195788288     29195804671   8.0 MiB     BF07

Still no change here though:

# zpool list
tank  8.12T  7.78T   349G    95%  1.04x  ONLINE  -

Does the resizing take a while? I can't see anything reporting an ongoing operation.

The relevant zfsonlinux issue has been resolved two years ago (notice the comment claiming two of the methods I failed with here worked).

Using zfsutils zfs-dkms Version: 0.6.2-1~saucy

share|improve this question
up vote 1 down vote accepted

You will need to either unload the ZFS module and reinsert it or just reboot.

Following that, you can run zpool online -e devicename and see the new zpool size.

However, I should add that I often use ZFS atop hardware RAID... But using it on top of MD software RAID doesn't make much sense unless you have some other constraints.

share|improve this answer
I would have used raidz, if it had allowed me to resize the array... – pascal Jan 25 '14 at 0:48
so: zpool export; modprobe -r zfs; modprobe zfs; zpool import; zpool online -e tank md2 didn't change anything either – pascal Jan 25 '14 at 0:51
Reboot your system. – ewwhite Jan 25 '14 at 1:01

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