Regarding the mon_osd_min_down_reports I was looking at it recently, this could provide some insight https://github.com/ceph/ceph/commit/0269a0c17723fd3e22738f7495fe017225b924a4 Thanks! On 10/17/16, 1:36 PM, "ceph-users on behalf of Somnath Roy" <ceph-users-bounces@xxxxxxxxxxxxxx on behalf of Somnath.Roy@xxxxxxxxxxx> wrote: Thanks Piotr, Wido for quick response. @Wido , yes, I thought of trying with those values but I am seeing in the log messages at least 7 osds are reporting failure , so, didn't try. BTW, I found default mon_osd_min_down_reporters is 2 , not 1 and latest master is not having mon_osd_min_down_reports anymore. Not sure what it is replaced with.. @Piotr , yes, your PR really helps , thanks ! Regarding each messenger needs to respond to HB is confusing, I know each thread has a HB timeout value and beyond which it will crash with suicide timeout , are you talking about that ? Regards Somnath -----Original Message----- From: Piotr Dałek [mailto:branch@xxxxxxxxxxxxxxxx] Sent: Monday, October 17, 2016 12:52 AM To: ceph-users@xxxxxxxxxxxxxx; Somnath Roy; ceph-devel@xxxxxxxxxxxxxxx Subject: Re: OSDs are flapping and marked down wrongly On Mon, Oct 17, 2016 at 07:16:44AM +0000, Somnath Roy wrote: > Hi Sage et. al, > > I know this issue is reported number of times in community and attributed to either network issue or unresponsive OSDs. > Recently, we are seeing this issue when our all SSD cluster (Jewel based) is stressed with large block size and very high QD. Lowering QD it is working just fine. > We are seeing the lossy connection message like below and followed by the osd marked down by monitor. > > 2016-10-15 14:30:13.957534 7f6297bff700 0 -- 10.10.10.94:6810/2461767 > submit_message osd_op_reply(1463 > rbd_data.55246b8b4567.000000000000d633 [set-alloc-hint object_size > 4194304 write_size 4194304,write 3932160~262144] v222'95890 uv95890 > ondisk = 0) v7 remote, 10.10.10.98:0/1174431362, dropping message > > In the monitor log, I am seeing the osd is reported down by peers and subsequently monitor is marking it down. > OSDs is rejoining the cluster after detecting it is marked down wrongly and rebalancing started. This is hurting performance very badly. > > My question is the following. > > 1. I have 40Gb network and I am seeing network is not utilized beyond 10-12Gb/s , no network error is reported. So, why this lossy connection message is coming ? what could go wrong here ? Is it network prioritization issue of smaller ping packets ? I tried to gaze ping round time during this and nothing seems abnormal. > > 2. Nothing is saturated on the OSD side , plenty of network/memory/cpu/disk is left. So, I doubt my osds are unresponsive but yes it is really busy on IO path. Heartbeat is going through separate messenger and threads as well, so, busy op threads should not be making heartbeat delayed. Increasing osd heartbeat grace is only delaying this phenomenon , but, eventually happens after several hours. Anything else we can tune here ? There's a bunch of messengers in OSD code, if ANY of them doesn't respond to heartbeat messages in reasonable time, it is marked as down. Since packets are processed in FIFO/synchronous manner, overloading OSD with large I/O will cause it to time-out on at least one messenger. There was an idea to have heartbeat messages go in the OOB TCP/IP stream and process them asynchronously, but I don't know if that went beyond the idea stage. > 3. What could be the side effect of big grace period ? I understand that detecting a faulty osd will be delayed, anything else ? Yes - stalled ops. Assume that primary OSD goes down and replicas are still alive. Having big grace period will cause all ops going to that OSD to stall until that particular OSD is marked down or resumes normal operation. > 4. I saw if an OSD is crashed, monitor will detect the down osd almost instantaneously and it is not waiting till this grace period. How it is distinguishing between unresponsive and crashed osds ? In which scenario this heartbeat grace is coming into picture ? This is the effect of my PR#8558 (https://github.com/ceph/ceph/pull/8558) which causes any OSD that crash to be immediately marked as down, preventing stalled I/Os in most common cases. Grace period is only applied to unresponsive OSDs (i.e. temporary packet loss, bad cases of network lags, routing issues, in other words, everything that is known to be at least possible to resolve by itself in a finite amount of time). OSDs that crash and burn won't respond - instead, OS will respond with ECONNREFUSED indicating that OSD is not listening and in that case the OSD will be immediately marked down. -- Piotr Dałek branch@xxxxxxxxxxxxxxxx http://blog.predictor.org.pl PLEASE NOTE: The information contained in this electronic mail message is intended only for the use of the designated recipient(s) named above. If the reader of this message is not the intended recipient, you are hereby notified that you have received this message in error and that any review, dissemination, distribution, or copying of this message is strictly prohibited. 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