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 
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 -- 
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,, dropping 

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 

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 ?

3. What could be the side effect of big grace period ? I understand that 
detecting a faulty osd will be delayed, anything else ?

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 ?

Any help on clarifying this would be very helpful.

Thanks & Regards
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. 
If you have received this communication in error, please notify the sender by 
telephone or e-mail (as shown above) immediately and destroy any and all copies 
of this message in your possession (whether hard copies or electronically 
stored copies).
ceph-users mailing list

Reply via email to