@olivierlambert
Hmm, if we creating a volume plugin that combine linux cgroups (iops/bandwidth limit) + filesystem (zfs block device - zvol), that would be one possible workaround no matter what's at the bottom.

SMAPI v3 looks very exciting, unfortunately on the bottom is still tapdisk, and that has one but it's a very serious limitation - no io/bandwidth limit ;(

Where in xoa can I change device position, I cannot find this option.

In XenCenter this option is available in Storage -> Properties