kernel.pid_max=4194303
fs.file-max=26234859
vm.zone_reclaim_mode=0
vm.vfs_cache_pressure=50
vm.min_free_kbytes=4194303
Craig Chi
Hi Craig,
From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of Craig Chi
Sent: 24 November 2016 08:34
To: ceph-users@xxxxxxxxxxxxxx
Subject: Ceph OSDs cause kernel unresponsive
Hi Cephers,
We have encountered kernel hanging issue on our Ceph cluster. Just like http://imgur.com/a/U2Flz , http://imgur.com/a/lyEko or http://imgur.com/a/IGXdu .
We believed it is caused by out of memory, because we observed that when OSDs went crazy, the available memory of each node were decreasing rapidly (from 50% available to lower than 10%). Then the node running Ceph OSD became unresponsive with console showing hung_task_timout or slab_out_of_memory, etc. The only thing we can do then is hard reset the unit.
It is hard to predict when the kernel hanging issue will happen. In my past experiences, it usually happened after a long term benchmark procedure, and followed by a manual trigger like 1) reboot a node 2) restart all OSDs 3) modify CRUSH map.
Currently the cluster is back to normal, but we want to figure out the root cause to avoid happening again. We think the high values of ceph.conf are pretty suspicous, but without code tracing we are hard to realize the impact of the values and the memory consumption.
Many thanks if you have any suggestions.
I think you are probably running out of memory, 90x8TB disks is 720Tb of storage, that will need a lot of ram to run and also the fact that the problems occur when PG’s start moving around after a node failure also suggests this.
Have you adjusted your vm.vfs_cache_pressure?
You might also want to try setting vm.min_free_kbytes to 8-16GB to try and keep some memory free and avoid fragmentation.
=================================================================================
Following is our ceph cluster architecture:
OS: Ubuntu 16.04.1 LTS (4.4.0-31-generic #50-Ubuntu x86_64 GNU/Linux)
Ceph: Jewel 10.2.3
3 Ceph Monitors running on 3 dedicated machines
630 Ceph OSDs running on 7 storage machines (each machine has 256GB RAM and 90 units of 8TB hard drives)
There are 4 pools with following settings:
vms 512 pg x 3 replica
images 512 pg x 3 replica
volumes 8192 pg x 3 replica
objects 4096 pg x (17,3) erasure code profile
==> average 173.92 pgs per OSD
We tuned our ceph.conf by referencing many performance tuning resources online ( mainly from slide 38 of https://goo.gl/Idkh41 )
[global]
osd pool default pg num = 4096
osd pool default pgp num = 4096
err to syslog = true
log to syslog = true
osd pool default size = 3
max open files = 131072
fsid = 1c33bf75-e080-4a70-9fd8-860ff216f595
osd crush chooseleaf type = 1
[mon.mon1]
host = mon1
mon addr = 172.20.1.2
[mon.mon2]
host = mon2
mon addr = 172.20.1.3
[mon.mon3]
host = mon3
mon addr = 172.20.1.4
[mon]
mon osd full ratio = 0.85
mon osd nearfull ratio = 0.7
mon osd down out interval = 600
mon osd down out subtree limit = host
mon allow pool delete = true
mon compact on start = true
[osd]
public_network = 172.20.3.1/21
cluster_network = 172.24.0.1/24
osd disk threads = 4
osd mount options xfs = rw,noexec,nodev,noatime,nodiratime,nobarrier,inode64,logbsize=256k
osd crush update on start = false
osd op threads = 20
osd mkfs options xfs = -f -i size=2048
osd max write size = 512
osd mkfs type = xfs
osd journal size = 5120
filestore max inline xattrs = 6
filestore queue committing max bytes = 1048576000
filestore queue committing max ops = 5000
filestore queue max bytes = 1048576000
filestore op threads = 32
filestore max inline xattr size = 254
filestore max sync interval = 15
filestore min sync interval = 10
journal max write bytes = 1048576000
journal max write entries = 1000
journal queue max ops = 3000
journal queue max bytes = 1048576000
ms dispatch throttle bytes = 1048576000
Sincerely,
Craig Chi
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