[ovirt-devel] Reporting vm disk stats "truesize" and "apparentsize"?

[Michal Skrivanek]

> On 15 Sep 2016, at 18:18, Nir Soffer <nsoffer at redhat.com> wrote:
> 
> Hi all,
> 
> Vdsm reports apparentsize and truesize disk stats [1] when getting
> vms stats (every 15 seconds?). These values are update every
> 60 seconds in vdsm.
> 
> To collect the values, we run risky storage apis in vdsm virt thread
> pool, and we want to avoid this [2] since one slow or broken domain
> can cause the entire virt thread pool to get stuck and cause vms
> using other (healthy) storage domain to become non responsive.
> 
> These can also break block storage thin provisioned disks, since they
> depend also on the virt thread pool. So one bad NFS storage domain
> can cause vms using only block storage to be paused.
> 
> If both of these values are not used by anyone, we would like to
> stop reporting them.

there are only 2 consumers of the monitoring, engine and mom.
git grep reveals that “apparentsize" is used only for importing HE.
“truesize" too, but additionally it is used in engine storage code as an actual size of the disk

> 
> If the values are used, we need to find a safer way to report them,
> probably in storage thread pool, or maybe we can get these values
> from libvirt using bulk sampling.

you could have been able to drop apparentsize right away, but the HE import code is expecting that field and won’t be happy if it is missing
The monitoring code would work but fill in 0 for the actual size

> 
> Please update if these values are used in engine/dwh.
> 
> [1] https://github.com/oVirt/vdsm/blob/master/lib/vdsm/virt/vmstats.py#L364
> [2] https://gerrit.ovirt.org/59801
> 
> Nir
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