I never actually set up iSCSI with VMware, I just had to research various VMware storage options when we had a SAN-probelm at a former job... But I can take a look at it again if you want me to. Is it realy deadlocked when this issue occurs? What I think is partly responsible for this situation is that the iSCSI LUN queues fill up and that's what actually kills your IO - VMware lowers queue depth to 1 in that situation and it can take a really long time to recover (especially if one of the LUNs on the target constantly has problems, or when heavy IO hammers the adapter) - you should never fill this queue, ever. iSCSI will likely be innocent victim in the chain, not the cause of the issues. Ceph should gracefully handle all those situations, you just need to set the timeouts right. I have it set so that whatever happens the OSD can only delay work for 40s and then it is marked down - at that moment all IO start flowing again. You should take this to VMware support, they should be able to tell whether the problem is in iSCSI target (then you can take a look at how that behaves) or in the initiator settings. Though in my experience after two visits from their "foremost experts" I had to google everything myself because they were clueless - YMMV. The root cause is however slow ops in Ceph, and I have no idea why you'd have them if the OSDs come back up - maybe one of them is really deadlocked or backlogged in some way? I found that when OSDs are "dead but up" they don't respond to "ceph tell osd.xxx ..." so try if they all respond in a timely manner, that should help pinpoint the bugger. Jan > On 24 Aug 2015, at 18:26, Alex Gorbachev <ag@xxxxxxxxxxxxxxxxxxx> wrote: > >> This can be tuned in the iSCSI initiation on VMware - look in advanced settings on your ESX hosts (at least if you use the software initiator). > > Thanks, Jan. I asked this question of Vmware as well, I think the > problem is specific to a given iSCSI session, so wondering if that's > strictly the job of the target? Do you know of any specific SCSI > settings that mitigate this kind of issue? Basically, give up on a > session and terminate it and start a new one should an RBD not > respond? > > As I understand, RBD simply never gives up. If an OSD does not > respond but is still technically up and in, Ceph will retry IOs > forever. I think RBD and Ceph need a timeout mechanism for this. > > Best regards, > Alex > >> Jan >> >> >>> On 23 Aug 2015, at 21:28, Nick Fisk <nick@xxxxxxxxxx> wrote: >>> >>> Hi Alex, >>> >>> Currently RBD+LIO+ESX is broken. >>> >>> The problem is caused by the RBD device not handling device aborts properly >>> causing LIO and ESXi to enter a death spiral together. >>> >>> If something in the Ceph cluster causes an IO to take longer than 10 >>> seconds(I think!!!) ESXi submits an iSCSI abort message. Once this happens, >>> as you have seen it never recovers. >>> >>> Mike Christie from Redhat is doing a lot of work on this currently, so >>> hopefully in the future there will be a direct RBD interface into LIO and it >>> will all work much better. >>> >>> Either tgt or SCST seem to be pretty stable in testing. >>> >>> Nick >>> >>>> -----Original Message----- >>>> From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of >>>> Alex Gorbachev >>>> Sent: 23 August 2015 02:17 >>>> To: ceph-users <ceph-users@xxxxxxxxxxxxxx> >>>> Subject: Slow responding OSDs are not OUTed and cause RBD >>>> client IO hangs >>>> >>>> Hello, this is an issue we have been suffering from and researching along >>>> with a good number of other Ceph users, as evidenced by the recent posts. >>>> In our specific case, these issues manifest themselves in a RBD -> iSCSI >>> LIO -> >>>> ESXi configuration, but the problem is more general. >>>> >>>> When there is an issue on OSD nodes (examples: network hangs/blips, disk >>>> HBAs failing, driver issues, page cache/XFS issues), some OSDs respond >>>> slowly or with significant delays. ceph osd perf does not show this, >>> neither >>>> does ceph osd tree, ceph -s / ceph -w. Instead, the RBD IO hangs to a >>> point >>>> where the client times out, crashes or displays other unsavory behavior - >>>> operationally this crashes production processes. >>>> >>>> Today in our lab we had a disk controller issue, which brought an OSD node >>>> down. Upon restart, the OSDs started up and rejoined into the cluster. >>>> However, immediately all IOs started hanging for a long time and aborts >>> from >>>> ESXi -> LIO were not succeeding in canceling these IOs. The only warning >>> I >>>> could see was: >>>> >>>> root@lab2-mon1:/var/log/ceph# ceph health detail HEALTH_WARN 30 >>>> requests are blocked > 32 sec; >>>> 1 osds have slow requests 30 ops are blocked > 2097.15 sec >>>> 30 ops are blocked > 2097.15 sec on osd.4 >>>> 1 osds have slow requests >>>> >>>> However, ceph osd perf is not showing high latency on osd 4: >>>> >>>> root@lab2-mon1:/var/log/ceph# ceph osd perf osd fs_commit_latency(ms) >>>> fs_apply_latency(ms) >>>> 0 0 13 >>>> 1 0 0 >>>> 2 0 0 >>>> 3 172 208 >>>> 4 0 0 >>>> 5 0 0 >>>> 6 0 1 >>>> 7 0 0 >>>> 8 174 819 >>>> 9 6 10 >>>> 10 0 1 >>>> 11 0 1 >>>> 12 3 5 >>>> 13 0 1 >>>> 14 7 23 >>>> 15 0 1 >>>> 16 0 0 >>>> 17 5 9 >>>> 18 0 1 >>>> 19 10 18 >>>> 20 0 0 >>>> 21 0 0 >>>> 22 0 1 >>>> 23 5 10 >>>> >>>> SMART state for osd 4 disk is OK. The OSD in up and in: >>>> >>>> root@lab2-mon1:/var/log/ceph# ceph osd tree >>>> ID WEIGHT TYPE NAME UP/DOWN REWEIGHT PRIMARY-AFFINITY >>>> -8 0 root ssd >>>> -7 14.71997 root platter >>>> -3 7.12000 host croc3 >>>> 22 0.89000 osd.22 up 1.00000 1.00000 >>>> 15 0.89000 osd.15 up 1.00000 1.00000 >>>> 16 0.89000 osd.16 up 1.00000 1.00000 >>>> 13 0.89000 osd.13 up 1.00000 1.00000 >>>> 18 0.89000 osd.18 up 1.00000 1.00000 >>>> 8 0.89000 osd.8 up 1.00000 1.00000 >>>> 11 0.89000 osd.11 up 1.00000 1.00000 >>>> 20 0.89000 osd.20 up 1.00000 1.00000 >>>> -4 0.47998 host croc2 >>>> 10 0.06000 osd.10 up 1.00000 1.00000 >>>> 12 0.06000 osd.12 up 1.00000 1.00000 >>>> 14 0.06000 osd.14 up 1.00000 1.00000 >>>> 17 0.06000 osd.17 up 1.00000 1.00000 >>>> 19 0.06000 osd.19 up 1.00000 1.00000 >>>> 21 0.06000 osd.21 up 1.00000 1.00000 >>>> 9 0.06000 osd.9 up 1.00000 1.00000 >>>> 23 0.06000 osd.23 up 1.00000 1.00000 >>>> -2 7.12000 host croc1 >>>> 7 0.89000 osd.7 up 1.00000 1.00000 >>>> 2 0.89000 osd.2 up 1.00000 1.00000 >>>> 6 0.89000 osd.6 up 1.00000 1.00000 >>>> 1 0.89000 osd.1 up 1.00000 1.00000 >>>> 5 0.89000 osd.5 up 1.00000 1.00000 >>>> 0 0.89000 osd.0 up 1.00000 1.00000 >>>> 4 0.89000 osd.4 up 1.00000 1.00000 >>>> 3 0.89000 osd.3 up 1.00000 1.00000 >>>> >>>> How can we proactively detect this condition? Is there anything I can run >>>> that will output all slow OSDs? >>>> >>>> Regards, >>>> Alex >>>> _______________________________________________ >>>> ceph-users mailing list >>>> ceph-users@xxxxxxxxxxxxxx >>>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >>> >>> >>> >>> >>> _______________________________________________ >>> ceph-users mailing list >>> ceph-users@xxxxxxxxxxxxxx >>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >> _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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