On 4 Oct 2016, at 09:51, Gary Lloyd <g.lloyd(a)keele.ac.uk&gt; 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 ?

Also is there anything that we can tweak to automatically unpause the VMs once connectivity with the arrays is re-established ?

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. Many Thanks Gary Lloyd ________________________________________________ I.T. Systems:Keele University Finance & IT Directorate Keele:Staffs:IC1 Building:ST5 5NB:UK +44 1782 733063 ________________________________________________ _______________________________________________ Users mailing list Users(a)ovirt.org http://lists.ovirt.org/mailman/listinfo/users

> On 4 Oct 2016, at 09:51, Gary Lloyd <g.lloyd(a)keele.ac.uk&gt; 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 ? not really. but things are not so different when you look at it from the guest perspective. If the intention is to hide the fact that there is a problem and the guest should just see a delay (instead of dealing with error) then pausing and unpausing is the right behavior. From guest point of view this is just a delay it sees. > > Also is there anything that we can tweak to automatically unpause the VMs once connectivity with the arrays is re-established ? that should happen when the storage domain monitoring detects error and then reactivate(http://gerrit.ovirt.org/16244). It may be that since you have direct luns it’s not working with those….dunno, storage people should chime in I guess...

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(a)redhat.com <mailto:nsoffer@redhat.com>> wrote: On Tue, Oct 4, 2016 at 10:51 AM, Gary Lloyd <g.lloyd(a)keele.ac.uk <mailto:g.lloyd@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 _______________________________________________ Users mailing list Users(a)ovirt.org http://lists.ovirt.org/mailman/listinfo/users

From the sounds of it the best we can do then is to use a 60 second timeout

On Thu, Oct 6, 2016 at 10:19 AM, Gary Lloyd <g.lloyd(a)keele.ac.uk&gt; wrote: > 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 ? > Yes, we cannot work with unlimited queue. This will block vdsm for unlimited time when the next command try to access storage. Because we don't have good isolation between different storage domains, this may cause other storage domains to become faulty. Also engine flows that have a timeout will fail with a timeout. If you are on 3.x, this will be very painfull, on 4.0 it should be better, but it is not recommended. Nir