On Wed, Oct 9, 2019 at 2:55 PM Francesco Romani <from...@redhat.com> wrote:
> On 10/8/19 4:06 PM, Gianluca Cecchi wrote:
>
> Hi Gianluca
>
> > Hello,
> > I'm doing some tests related to storage latency or problems manually
> > created to debug and manage reactions of hosts and VMs.
> > What is the subsystem/process/daemon responsible to pause a VM when
> > problems arise on storage for the host where the VM is running?
>
>
> It's Vdsm itself.
>
ok
>
>
> > How is determined the timeout to use to put the VM in pause mode?
>
>
> The VM is paused immediately as soon as libvirt, through QEMU, reports
> IOError, to avoid data corruption. Now, when libvirt reports this error
>
> depends laregly on the timeout set for the storage configuration, which
> is done at host level, using system tools (e.g. it is not a Vdsm tunable)
>
>
For test I have set this in multipath.conf of host:
devices {
device {
all_devs yes
# Set timeout of queuing of 5*28 = 140 seconds
# similar to vSphere APD timeout
# no_path_retry fail
no_path_retry 28
polling_interval 5
}
So it should wait at least 140 seconds before passing error to upper layer
correct?
> > Sometimes I see after clearing the problems that the VM is
> > automatically un-paused, sometimes no: how is this managed?
>
>
I noticed that if I set disk as virtio-scsi (it seems virtio has no timeout
definable and passes suddenly the error to upper layer) and disk timeout of
vm disk (through udev rule) to 180 seconds, I can block access to the
storage for example for 100 seconds and the host is able to reinstate paths
and then vm is always unpaused.
But I would like to prevent VM from pausing at all
What else to tweak?
Thanks,
Gianluca
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