[docs] Cannot start vm from disk with burst qos

[Vladislav Belogrudov]

when trying to run a VM from a disk associated with burst qos consumer=both total_iops_sec_max=200 , nova/libvirt reports:

Failed to start libvirt guest: libvirt.libvirtError: internal error: unable to execute QEMU command 'block_set_io_throttle': bps_max/iops_max require corresponding bps/iops values

Also when setting up size_iops_sec:
nova.virt.libvirt.guest libvirt.libvirtError: internal error: unable to execute QEMU command 'block_set_io_throttle': iops size requires an iops value to be set

OpenStack Yoga, CentOS Stream 8
libvirt 8.0.0-2
qemu 6.2.0-5
cinder backend: lvm (can be any other iscsi storage as well)

[Vladislav Belogrudov (vlad-belogrudov)]

it looks like incorrect/incomplete documentation.
According to https://github.com/qemu/qemu/blob/master/docs/throttle.txt for burst max values it is necessary to also provide period and normal limits.

[Balazs Gibizer (balazs-gibizer)]

Nova only acts based on the qos policy from cinder. So I'm moving this bug to cinder. I suspect that this is either a doc bug on cinder to state in the doc that these qos configs needs to be set together (e.g. total_iops_sec_max needs to be set together with total_iops_sec) or maybe a cinder change that validates on the qos API that valid pairs are set.