[ovirt-users] VMs paused due to IO issues - Dell Equallogic controller failover

Thu Oct 6 08:16:14 UTC 2016

you need the eql hit kit to make it work at least somehow better, but
hit kit requires multipathd to be disabled which is an dependency to ovirt.

so far, no real workaround seems to be known

Am 06.10.2016 um 09:19 schrieb Gary Lloyd:
> I asked on the Dell Storage Forum and they recommend the following:
> 
> /I recommend not using a numeric value for the "no_path_retry" variable
> within /etc/multipath.conf as once that numeric value is reached, if no
> healthy LUNs were discovered during that defined time multipath will
> disable the I/O queue altogether./
> 
> /I do recommend, however, changing the variable value from "12" (or even
> "60") to "queue" which will then allow multipathd to continue queing I/O
> until a healthy LUN is discovered (time of fail-over between
> controllers) and I/O is allowed to flow once again./
> 
> Can you see any issues with this recommendation as far as Ovirt is
> concerned ?
> 
> Thanks again
> 
> 
> /Gary Lloyd/
> ________________________________________________
> I.T. Systems:Keele University
> Finance & IT Directorate
> Keele:Staffs:IC1 Building:ST5 5NB:UK
> +44 1782 733063 <tel:%2B44%201782%20733073>
> ________________________________________________
> 
> On 4 October 2016 at 19:11, Nir Soffer <nsoffer at redhat.com
> <mailto:nsoffer at redhat.com>> wrote:
> 
>     On Tue, Oct 4, 2016 at 10:51 AM, Gary Lloyd <g.lloyd at keele.ac.uk
>     <mailto:g.lloyd at keele.ac.uk>> wrote:
> 
>         Hi
> 
>         We have Ovirt 3.65 with a Dell Equallogic SAN and we use Direct
>         Luns for all our VMs.
>         At the weekend during early hours an Equallogic controller
>         failed over to its standby on one of our arrays and this caused
>         about 20 of our VMs to be paused due to IO problems.
> 
>         I have also noticed that this happens during Equallogic firmware
>         upgrades since we moved onto Ovirt 3.65.
> 
>         As recommended by Dell disk timeouts within the VMs are set to
>         60 seconds when they are hosted on an EqualLogic SAN.
> 
>         Is there any other timeout value that we can configure in
>         vdsm.conf to stop VMs from getting paused when a controller
>         fails over ?
> 
> 
>     You can set the timeout in multipath.conf.
> 
>     With current multipath configuration (deployed by vdsm), when all
>     paths to a device
>     are lost (e.g. you take down all ports on the server during
>     upgrade), all io will fail
>     immediately.
> 
>     If you want to allow 60 seconds gracetime in such case, you can
>     configure:
> 
>         no_path_retry 12
> 
>     This will continue to monitor the paths 12 times, each 5 seconds 
>     (assuming polling_interval=5). If some path recover during this
>     time, the io
>     can complete and the vm will not be paused.
> 
>     If no path is available after these retries, io will fail and vms
>     with pending io
>     will pause.
> 
>     Note that this will also cause delays in vdsm in various flows,
>     increasing the chance
>     of timeouts in engine side, or delays in storage domain monitoring.
> 
>     However, the 60 seconds delay is expected only on the first time all
>     paths become
>     faulty. Once the timeout has expired, any access to the device will
>     fail immediately.
> 
>     To configure this, you must add the # VDSM PRIVATE tag at the second
>     line of
>     multipath.conf, otherwise vdsm will override your configuration in
>     the next time
>     you run vdsm-tool configure.
> 
>     multipath.conf should look like this:
> 
>     # VDSM REVISION 1.3
>     # VDSM PRIVATE
> 
>     defaults {
>         polling_interval            5
>         no_path_retry               12
>         user_friendly_names         no
>         flush_on_last_del           yes
>         fast_io_fail_tmo            5
>         dev_loss_tmo                30
>         max_fds                     4096
>     }
> 
>     devices {
>         device {
>             all_devs                yes
>             no_path_retry           12
>         }
>     }
> 
>     This will use 12 retries (60 seconds) timeout for any device. If you
>     like to 
>     configure only your specific device, you can add a device section for
>     your specific server instead.
>      
> 
> 
>         Also is there anything that we can tweak to automatically
>         unpause the VMs once connectivity with the arrays is
>         re-established ?
> 
> 
>     Vdsm will resume the vms when storage monitor detect that storage
>     became available again.
>     However we cannot guarantee that storage monitoring will detect that
>     storage was down.
>     This should be improved in 4.0.
>      
> 
>         At the moment we are running a customized version of
>         storageServer.py, as Ovirt has yet to include iscsi multipath
>         support for Direct Luns out of the box.
> 
> 
>     Would you like to share this code?
> 
>     Nir
> 
> 
> 
> 
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