Growing a VirtualBox disk with ZFS on it

I have a VirtualBox VM on a Windows host with a 32 GB disk. That disk is partitioned with GPT and has four partitions: a boot partition, a swap partition, a smallish UFS root partition, and a ZFS partition. I need more space in the latter, so let’s grow it.

The first step is to shut down the VM and resize the virtual disk. This cannot be done in the GUI—we have to use the command-line utility:

C:\Users\des\VirtualBox VMs\FreeBSD\CrashBSD 9>"\Program Files\Oracle\VirtualBox\VBoxManage.exe" showhdinfo "CrashBSD 9.vdi"
UUID:                 4a088148-72ef-4737-aae6-0a39e05aee06
Accessible:           yes
Logical size:         32768 MBytes
Current size on disk: 14484 MBytes
Type:                 normal (base)
Storage format:       VDI
Format variant:       dynamic default
In use by VMs:        CrashBSD 9 (UUID: 06bbe99d-9118-4c11-b29b-4ffd175ad06c)
Location:             C:\Users\des\VirtualBox VMs\FreeBSD\CrashBSD 9\CrashBSD 9.vdi

C:\Users\des\VirtualBox VMs\FreeBSD\CrashBSD 9>"\Program Files\Oracle\VirtualBox\VBoxManage.exe" modifyhd "CrashBSD 9.vdi" --resize 65536
0%...10%...20%...30%...40%...50%...60%...70%...80%...90%...100%

C:\Users\des\VirtualBox VMs\FreeBSD\CrashBSD 9>"\Program Files\Oracle\VirtualBox\VBoxManage.exe" showhdinfo "CrashBSD 9.vdi"
UUID:                 4a088148-72ef-4737-aae6-0a39e05aee06
Accessible:           yes
Logical size:         65536 MBytes
Current size on disk: 14485 MBytes
Type:                 normal (base)
Storage format:       VDI
Format variant:       dynamic default
In use by VMs:        CrashBSD 9 (UUID: 06bbe99d-9118-4c11-b29b-4ffd175ad06c)
Location:             C:\Users\des\VirtualBox VMs\FreeBSD\CrashBSD 9\CrashBSD 9.vdi

Next, we boot the VM into single-user mode. It will repeatedly complain about the secondary GPT table, which is supposed to be located at the end of the disk but is now in the middle, since we doubled the size of the disk:

GEOM: ada0: the secondary GPT header is not in the last LBA.
# gpart list ada0
Geom name: ada0
modified: false
state: CORRUPT
fwheads: 16
fwsectors: 63
last: 67108830
first: 34
entries: 128
scheme: GPT
Providers:
[...]

Thankfully, this is trivial to fix. In fact, this exact use case is mentioned in the gpart(8) man page:

# gpart ada0 recover
ada0 recovered.
# gpart list ada0
Geom name: ada0
modified: false
state: OK
fwheads: 16
fwsectors: 63
last: 134217694
first: 34
entries: 128
scheme: GPT
Providers:
[...]

Next, we resize the ZFS partition to fill all available space:

# gpart list ada0
[...]
4. Name: ada0p4
   Mediasize: 25769803776 (24G)
[...]
# gpart resize -i 4 ada0
ada0p4 resized
# gpart list ada0
[...]
4. Name: ada0p4
   Mediasize: 60129442304 (56G)
[...]

Let’s see what our pool looks like now:

# zpool import crash
# zfs list crash
NAME    USED  AVAIL  REFER  MOUNTPOINT
crash  14.2G  9.31G    31K  /

Hmm, no cigar. The pool hasn’t grown because the underlying vdev hasn’t automatically expanded to fill the resized partition. That’s easy to fix, though:

# zpool online -e crash ada0p4

And there we go:

# zfs list crash
NAME    USED  AVAIL  REFER  MOUNTPOINT
crash  14.2G  40.8G    31K  /

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