[lxc-users] LXD with ZFS and limiting block I/O resources

St├ęphane Graber stgraber at ubuntu.com
Wed May 25 14:50:32 UTC 2016

On Wed, May 25, 2016 at 04:23:07PM +0200, tapczan wrote:
> Hello
> As I understand ZFS is recommended filesystem for LXD. However is that
> possible that limiting block I/O resources on ZFS is not working?
> # lxc info | grep zfs
>   storage: zfs
>   storage.zfs_pool_name: lxd
> # lxc config device set c1 root limits.read 10MB
> error: Block device doesn't support quotas: 10:55
> I'm aware of compatibility issues with ZFS io throttling via cgroup:
> https://github.com/zfsonlinux/zfs/issues/1952
> https://github.com/zfsonlinux/zfs/issues/4275
> Am I missing something or limiting block I/O resources is really
> currently impossible?
> Thanks!

Can you check through /dev for the device with:
 - type: block
 - major: 10
 - minor: 55

Seems like LXD thinks that's what's backing your ZFS and the kernel
doesn't think it's a real block device so can't apply I/O quotas on it.

In general, the LXD code does figure out what the backing devices are
for your zpool and lets you set blkio limits on it. Whether zfs respects
them is a whole different problem though :)

St├ęphane Graber
Ubuntu developer
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