Re: [ovirt-users] VMs becoming non-responsive sporadically

On Sat, Apr 30, 2016 at 7:16 PM, <nicolas(a)devels.es&gt; wrote: > El 2016-04-30 16:55, Nir Soffer escribió: >> >> On Sat, Apr 30, 2016 at 11:33 AM, Nicolás <nicolas(a)devels.es&gt; wrote: >>> >>> Hi Nir, >>> >>> El 29/04/16 a las 22:34, Nir Soffer escribió: >>>> >>>> >>>> On Fri, Apr 29, 2016 at 9:17 PM, <nicolas(a)devels.es&gt; wrote: >>>>> >>>>> >>>>> Hi, >>>>> >>>>> We're running oVirt 3.6.5.3-1 and lately we're experiencing some issues >>>>> with >>>>> some VMs being paused because they're marked as non-responsive. Mostly, >>>>> after a few seconds they recover, but we want to debug precisely this >>>>> problem so we can fix it consistently. >>>>> >>>>> Our scenario is the following: >>>>> >>>>> ~495 VMs, of which ~120 are constantly up >>>>> 3 datastores, all of them iSCSI-based: >>>>> * ds1: 2T, currently has 276 disks >>>>> * ds2: 2T, currently has 179 disks >>>>> * ds3: 500G, currently has 65 disks >>>>> 7 hosts: All have mostly the same hardware. CPU and memory are >>>>> currently >>>>> very lowly used (< 10%). >>>>> >>>>> ds1 and ds2 are physically the same backend which exports two 2TB >>>>> volumes. >>>>> ds3 is a different storage backend where we're currently migrating some >>>>> disks from ds1 and ds2. >>>> >>>> >>>> What the the storage backend behind ds1 and 2? >>> >>> >>> >>> The storage backend for ds1 and ds2 is the iSCSI-based HP LeftHand P4000 >>> G2. >>> >>>>> Usually, when VMs become unresponsive, the whole host where they run >>>>> gets >>>>> unresponsive too, so that gives a hint about the problem, my bet is the >>>>> culprit is somewhere on the host side and not on the VMs side. >>>> >>>> >>>> Probably the vm became unresponsive because connection to the host was >>>> lost. >>> >>> >>> >>> I forgot to mention that less commonly we have situations where the host >>> doesn't get unresponsive but the VMs on it do and they don't become >>> responsive ever again, so we have to forcibly power them off and start >>> them >>> on a different host. But in this case the connection with the host >>> doesn't >>> ever get lost (so basically the host is Up, but any VM run on them is >>> unresponsive). >>> >>> >>>>> When that >>>>> happens, the host itself gets non-responsive and only recoverable after >>>>> reboot, since it's unable to reconnect. >>>> >>>> >>>> Piotr, can you check engine log and explain why host is not reconnected? >>>> >>>>> I must say this is not specific to >>>>> this oVirt version, when we were using v.3.6.4 the same happened, and >>>>> it's >>>>> also worthy mentioning we've not done any configuration changes and >>>>> everything had been working quite well for a long time. >>>>> >>>>> We were monitoring our ds1 and ds2 physical backend to see performance >>>>> and >>>>> we suspect we've run out of IOPS since we're reaching the maximum >>>>> specified >>>>> by the manufacturer, probably at certain times the host cannot perform >>>>> a >>>>> storage operation within some time limit and it marks VMs as >>>>> unresponsive. >>>>> That's why we've set up ds3 and we're migrating ds1 and ds2 to ds3. >>>>> When >>>>> we >>>>> run out of space on ds3 we'll create more smaller volumes to keep >>>>> migrating. >>>>> >>>>> On the host side, when this happens, we've run repoplot on the vdsm log >>>>> and >>>>> I'm attaching the result. Clearly there's a *huge* LVM response time >>>>> (~30 >>>>> secs.). >>>> >>>> >>>> Indeed the log show very slow vgck and vgs commands - these are called >>>> every >>>> 5 minutes for checking the vg health and refreshing vdsm lvm cache. >>>> >>>> 1. starting vgck >>>> >>>> Thread-96::DEBUG::2016-04-29 >>>> 13:17:48,682::lvm::290::Storage.Misc.excCmd::(cmd) /usr/bin/taskset >>>> --cpu-list 0-23 /usr/bin/sudo -n /usr/sbin/lvm vgck --config ' devices >>>> { pre >>>> ferred_names = ["^/dev/mapper/"] ignore_suspended_devices=1 >>>> write_cache_state=0 disable_after_error_count=3 filter = [ >>>> '\''a|/dev/mapper/36000eb3a4f1acbc20000000000000043|'\ >>>> '', '\''r|.*|'\'' ] } global { locking_type=1 >>>> prioritise_write_locks=1 wait_for_locks=1 use_lvmetad=0 } backup { >>>> retain_min = 50 retain_days = 0 } ' 5de4a000-a9c4-48 >>>> 9c-8eee-10368647c413 (cwd None) >>>> >>>> 2. vgck ends after 55 seconds >>>> >>>> Thread-96::DEBUG::2016-04-29 >>>> 13:18:43,173::lvm::290::Storage.Misc.excCmd::(cmd) SUCCESS: <err> = ' >>>> WARNING: lvmetad is running but disabled. Restart lvmetad before >>>> enabling it!\n'; <rc> = 0 >>>> >>>> 3. starting vgs >>>> >>>> Thread-96::DEBUG::2016-04-29 >>>> 13:17:11,963::lvm::290::Storage.Misc.excCmd::(cmd) /usr/bin/taskset >>>> --cpu-list 0-23 /usr/bin/sudo -n /usr/sbin/lvm vgs --config ' devices >>>> { pref >>>> erred_names = ["^/dev/mapper/"] ignore_suspended_devices=1 >>>> write_cache_state=0 disable_after_error_count=3 filter = [ >>>> '\''a|/dev/mapper/36000eb3a4f1acbc20000000000000043|/de >>>> >>>> >>>> v/mapper/36000eb3a4f1acbc200000000000000b9|/dev/mapper/360014056f0dc8930d744f83af8ddc709|/dev/mapper/WDC_WD5003ABYZ-011FA0_WD-WMAYP0J73DU6|'\'', >>>> '\''r|.*|'\'' ] } global { >>>> locking_type=1 prioritise_write_locks=1 wait_for_locks=1 >>>> use_lvmetad=0 } backup { retain_min = 50 retain_days = 0 } ' >>>> --noheadings --units b --nosuffix --separator '| >>>> ' --ignoreskippedcluster -o >>>> >>>> >>>> uuid,name,attr,size,free,extent_size,extent_count,free_count,tags,vg_mda_size,vg_mda_free,lv_count,pv_count,pv_name >>>> 5de4a000-a9c4-489c-8eee-10368 >>>> 647c413 (cwd None) >>>> >>>> 4. vgs finished after 37 seconds >>>> >>>> Thread-96::DEBUG::2016-04-29 >>>> 13:17:48,680::lvm::290::Storage.Misc.excCmd::(cmd) SUCCESS: <err> = ' >>>> WARNING: lvmetad is running but disabled. Restart lvmetad before >>>> enabling it!\n'; <rc> = 0 >>>> >>>> Zdenek, how do you suggest to debug this slow lvm commands? >>>> >>>> Can you run the following commands on a host in trouble, and on some >>>> other >>>> hosts in the same timeframe? >>>> >>>> time vgck -vvvv --config ' devices { filter = >>>> ['\''a|/dev/mapper/36000eb3a4f1acbc20000000000000043|'\'', >>>> '\''r|.*|'\'' ] } global { locking_type=1 prioritise_write_locks=1 >>>> wait_for_locks=1 use_lvmetad=0 } backup { retain_min = 50 >>>> retain_days = 0 } ' 5de4a000-a9c4-489c-8eee-10368647c413 >>>> >>>> time vgs -vvvv --config ' global { locking_type=1 >>>> prioritise_write_locks=1 wait_for_locks=1 use_lvmetad=0 } backup { >>>> retain_min = 50 retain_days = 0 } ' >>>> 5de4a000-a9c4-489c-8eee-10368647c413 >>>> >>>> Note that I added -vvvv to both commands, this will generate huge amount >>>> of debugging info. Please share the output of these commands. >>>> >>>> You may need to fix the commands. You can always copy and paste directly >>>> from vdsm log into the shell and add the -vvvv flag. >>>> >>> >>> Indeed, there seems to be a big difference on hosts 5 and 6. I'm >>> attaching >>> the results of the execution of both commands on all hosts. Both commands >>> show a pretty bigger output on hosts 5 and 6, and also a much bigger >>> execution time. Times are also attached in a file called TIMES. >>> >>>>> Our host storage network is correctly configured and on a 1G >>>>> interface, no errors on the host itself, switches, etc. >>>> >>>> >>>> 1G serving about 20-70 vms per host? (495 vms, 120 always up, 7 hosts)? >>>> >>>> Do you have separate network for management and storage, or both >>>> use this 1G interface? >>> >>> >>> >>> Yes, we have separate networks for management, storage and motion. >>> Storage >>> and motion have 1G each (plus, for storage we use a bond of 2 interfaces >>> in >>> ALB-mode (6)). Currently no host has more than 30 VMs at a time. >>> >>>>> We've also limited storage in QoS to use 10MB/s and 40 IOPS, >>>> >>>> >>>> How did you configure this limit? >>> >>> >>> >>> In the Data Center tab, I chose our DC and a QoS sub-tab appears, just >>> like >>> described here: http://www.ovirt.org/documentation/sla/network-qos/ >>> >>>> >>>>> but this issue >>>>> still happens, which leads me to be concerned whether this is not just >>>>> an >>>>> IOPS issue; each host handles about cca. 600 LVs. Could this be an >>>>> issue >>>>> too? I remark the LVM response times are low in normal conditions (~1-2 >>>>> seconds). >>>> >>>> >>>> We recommend to limit number lvs per vg to 350. If you have 276 disks on >>>> ds1, and the disks are using snapshots, you may have too many lvs, which >>>> can cause slowdowns in lvm operations. >>>> >>>> Can you share the output of: >>>> >>>> vdsm-tool dump-volume-chains 5de4a000-a9c4-489c-8eee-10368647c413 >>> >>> >>> >>> Ok, right now no VG has more than 350 VGs so I guess this is not >>> currently >>> the problem. Unfortunately, I run the vdsm-tool command but it didn't end >>> nor provide any output in cca. 1 hour, so I guess it was hanged and I >>> stopped it. If you confirm this is a normal execution time I can leave it >>> running whatever time it takes. >>> >>> host5:~# vgs >>> VG #PV #LV #SN Attr VSize VFree >>> 0927c050-6fb6-463c-bb37-8b8da641dcd3 1 63 0 wz--n- 499,62g 206,50g >>> 5de4a000-a9c4-489c-8eee-10368647c413 1 335 0 wz--n- 2,00t 518,62g >>> b13b9eac-1f2e-4a7e-bcd9-49f5f855c3d8 1 215 0 wz--n- 2,00t 495,25g >>> sys_vg 1 6 0 wz--n- 136,44g 122,94g >>>>> >>>>> >>>>> I'm attaching the vdsm.log, engine.log and repoplot PDF; >>>> >>>> >>>> This is very useful, thanks. Can you send also the vdsm logs and >>>> repoplots >>>> from other hosts for the same timeframe? >>>> >>>>> if someone could >>>>> give a hint on some additional problems in them and shed some light on >>>>> the >>>>> above thoughts I'd be very grateful. >>>> >>>> >>>> Do you have sar configured on the host? having sar logs can reveal more >>>> info about this timeframe. >>>> >>>> Do you have information about amount of io from vms during this >>>> timeframe? >>>> amount of io on the storage backend during this timeframe? >>> >>> >>> >>> Not currently, but I'll be alert for the time this happens again and I'll >>> check some sar commands related to I/O and I'll provide feedback. >>> Nevertheless, by the time I run the commands above no machine was >>> unresponsive and I'm still getting such huge execution times. I tried >>> running iotop now and I see there are 2 vgck and vgs processes with a >>> rate >>> of ~500Kb/s each for reading. >>> >>> root 24446 1.3 0.0 57008 6824 ? D< 09:15 0:00 >>> /usr/sbin/lvm vgs --config devices { preferred_names = ["^/dev/mapper/"] >>> ignore_suspended_devices=1 write_cache_state=0 >>> disable_after_error_count=3 >>> filter = [ >>> >>> 'a|/dev/mapper/36000eb3a4f1acbc20000000000000043|/dev/mapper/36000eb3a4f1acbc200000000000000b9|/dev/mapper/360014056f0dc8930d744f83af8ddc709|', >>> 'r|.*|' ] } global { locking_type=1 prioritise_write_locks=1 >>> wait_for_locks=1 use_lvmetad=0 } backup { retain_min = 50 retain_days >>> = 0 >>> } --noheadings --units b --nosuffix --separator | --ignoreskippedcluster >>> -o >>> >>> uuid,name,attr,size,free,extent_size,extent_count,free_count,tags,vg_mda_size,vg_mda_free,lv_count,pv_count,pv_name >>> b13b9eac-1f2e-4a7e-bcd9-49f5f855c3d >>> >>> I'm also attaching the iostat output for host 5 in a file called >>> iostat-host5. >> >> >> Interesting, all hosts are checking the same storage, but on host5 and >> host6 >> the output of vgs and vgck is 10 times bigger - this explain why they take >> about >> 10 times longer to run. >> >> $ ls -lh vgs-* >> -rw-r--r--. 1 nsoffer nsoffer 221K Apr 30 08:55 vgs-host1 >> -rw-r--r--. 1 nsoffer nsoffer 239K Apr 30 08:55 vgs-host2 >> -rw-r--r--. 1 nsoffer nsoffer 228K Apr 30 08:55 vgs-host3 >> -rw-r--r--. 1 nsoffer nsoffer 288K Apr 30 08:55 vgs-host4 >> -rw-r--r--. 1 nsoffer nsoffer 2.2M Apr 30 08:55 vgs-host5 >> -rw-r--r--. 1 nsoffer nsoffer 2.2M Apr 30 08:55 vgs-host6 >> -rw-r--r--. 1 nsoffer nsoffer 232K Apr 30 08:55 vgs-host7 >> $ ls -lh vgck-* >> -rw-r--r--. 1 nsoffer nsoffer 238K Apr 30 08:55 vgck-host1 >> -rw-r--r--. 1 nsoffer nsoffer 254K Apr 30 08:55 vgck-host2 >> -rw-r--r--. 1 nsoffer nsoffer 244K Apr 30 08:55 vgck-host3 >> -rw-r--r--. 1 nsoffer nsoffer 298K Apr 30 08:55 vgck-host4 >> -rw-r--r--. 1 nsoffer nsoffer 2.0M Apr 30 08:55 vgck-host5 >> -rw-r--r--. 1 nsoffer nsoffer 2.0M Apr 30 08:55 vgck-host6 >> -rw-r--r--. 1 nsoffer nsoffer 248K Apr 30 08:55 vgck-host7 >> >> Can you do collect the output of "dmsetup table -v" on host 1, 5, and 6? >> >> Nir > > > Sure, please find attached results of the command. Once again, for hosts 5 > and 6 the size is 10 times bigger than for host 1. I think the issue causing slow vgs and vgck commands is stale lvs on host 5 and 6. This may be the root caused for paused vms, but I cannot explain how it is related yet. Comparing vgck on host1 and host5 - we can see that vgck opens 213 /dev/mapper/* devices, actually 53 uniq devices, most of them are opened 4 times. On host5, vgck opens 2489 devices (622 uniq). This explains why the operation takes about 10 times longer. Checking dmsteup table output, we can see that host1 has 53 devices, and host5 622 devices. Checking the device open count, host1 has 15 stale devices (Open count: 0), but host5 has 597 stale devices. Leaving stale devices is a known issue, but we never had evidence that it cause trouble except warnings in lvm commands. Please open an ovirt bug about this issue, and include all the files you sent so far in this thread, and all the vdsm logs on host5. To remove the stale devices, you can do: for name in `dmsetup info -c -o open,name | awk '/ 0 / {print $2}'`; do echo "removing stale device: $name" dmsetup remove $name done

This will eliminate the slow lvm commands issue. The vm pausing issue may be related or not, lets see if make any difference. Nir