[ovirt-users] What recovers a VM from pause?

[Pavel Gashev]

Please note that it's necessary to add a magic line '# VDSM PRIVATE' as second line in /etc/multipath.conf. Otherwise vdsm would overwrite your settings.
Thus, /etc/multipath.conf should start with the following two lines:
# VDSM REVISION 1.3
# VDSM PRIVATE


On Mon, 2016-05-30 at 22:09 +0300, Nir Soffer wrote:

But you may modify multipath configuration on the host.

We use now this multipath configuration (/etc/multipath.conf):

# VDSM REVISION 1.3

defaults {
    polling_interval            5
    no_path_retry               fail
    user_friendly_names         no
    flush_on_last_del           yes
    fast_io_fail_tmo            5
    dev_loss_tmo                30
    max_fds                     4096
    deferred_remove             yes
}

devices {
    device {
        all_devs                yes
        no_path_retry           fail
    }
}

This enforces failing of io request on devices that by default will queue such
requests for long or unlimited time. Queuing requests is very bad for vdsm, and
cause various commands to block for minutes during storage outage,
failing various
flows in vdsm and the ui.
See https://bugzilla.redhat.com/880738

However, in your case, using queuing may be the best way to do the switch
from one storage to another in the smoothest way.

You may try this setting:

devices {
    device {
        all_devs                yes
        no_path_retry           30
    }
}

This will queue io requests for 30 seconds before failing.
Using this normally would be a bad idea with vdsm, since during storage outage,
vdsm may block for 30 seconds when no paths is available, and is not designed
for this behavior, but blocking from time to time for short time should be ok.

I think that modifying the configuration and reloading multipathd service should
be enough to use the new settings, but I'm not sure if this changes
existing sessions
or open devices.



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