zfs / zvol / partition does not show up

Written by
Walter Doekes
Published on 2021-01-01

On our Proxmox virtual machine I had to go into a volume to quickly fix an IP address. The volume exists on the VM host, so surely mounting is easy. Right?

I checked in /dev/zvol/pve2-pool/ where I found the disk:

# ls /dev/zvol/pve2-pool/vm-125-virtio0*
total 0
lrwxrwxrwx 1 root root 10 Dec 29 15:55 vm-125-virtio0 -> ../../zd48

Good, there's a disk:

# fdisk -l /dev/zd48
Disk /dev/zd48: 50 GiB, 53687091200 bytes, 104857600 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 8192 bytes
I/O size (minimum/optimal): 8192 bytes / 8192 bytes
Disklabel type: dos
Disk identifier: 0x000aec27

Device      Boot    Start       End  Sectors  Size Id Type
/dev/zd48p1 *        2048  97656831 97654784 46.6G 83 Linux
/dev/zd48p2      97656832 104855551  7198720  3.4G 82 Linux swap / Solaris

And it has partitions. Now if I could only find them, so I can mount them...

Apparently, there's a volmode on the ZFS volume that specifies how volumes should be exposed to the OS.

Setting it to full exposes volumes as fully fledged block devices, providing maximal functionality. [...] Setting it to dev hides its partitions. Volumes with property set to none are not exposed outside ZFS, but can be snapshoted, cloned, replicated, etc, that can be suitable for backup purposes.

So:

# zfs get volmode zl-pve2-ssd1/vm-125-virtio0
NAME                         PROPERTY  VALUE    SOURCE
zl-pve2-ssd1/vm-125-virtio0  volmode   default  default

# zfs set volmode=full zl-pve2-ssd1/vm-125-virtio0

# zfs get volmode zl-pve2-ssd1/vm-125-virtio0
NAME                         PROPERTY  VALUE    SOURCE
zl-pve2-ssd1/vm-125-virtio0  volmode   full     local

# ls -1 /dev/zl-pve2-ssd1/
vm-122-virtio0
vm-123-virtio0
vm-124-virtio0
vm-125-virtio0
vm-125-virtio0-part1
vm-125-virtio0-part2

Yes! Partitions for vm-125-virtio0.

If that partition does not show up as expected, a call to partx -a /dev/zl-pve2-ssd1/vm-125-virtio0 might do the trick.

Quick, do some mount /dev/zl-pve2-ssd1/vm-125-virtio0-part1 /mnt/root; edit some files.

But, try to refrain from editing the volume while the VM is running. That may cause filesystem corruption.

Lastly umount and unset the volmode again:

# zfs inherit volmode zl-pve2-ssd1/vm-125-virtio0

# zfs get volmode zl-pve2-ssd1/vm-125-virtio0
NAME                         PROPERTY  VALUE    SOURCE
zl-pve2-ssd1/vm-125-virtio0  volmode   default  default

And optionally updating kernel bookkeeping, with: partx -d -n 1:2 /dev/zl-pve2-ssd1/vm-125-disk-0

zfs / zvol / partition does not show up

zfs / zvol / partition does not show up

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