Re: Giant osd problems - loss of IO

Andrei Mikhailovsky <andrei@xxxxxxxxxx> · Tue, 9 Dec 2014 11:07:18 +0000 (GMT)

Following Jake's recommendation I have updated my sysctl.conf file and it seems to have helped with the problem of osds being marked down by other osd peers. It has been 3 days already. I am currently using the following settings in the sysctl.conf:

# Increase Linux autotuning TCP buffer limits
# Set max to 16MB for 1GE and 32M (33554432) or 54M (56623104) for 10GE
# Don't set tcp_mem itself! Let the kernel scale it based on RAM.
net.core.rmem_max = 134217728
net.core.wmem_max = 134217728
net.core.rmem_default = 134217728
net.core.wmem_default = 134217728
net.core.optmem_max = 134217728
net.ipv4.tcp_rmem = 4096 87380 67108864
net.ipv4.tcp_wmem = 4096 65536 67108864

# Make room for more TIME_WAIT sockets due to more clients,
# and allow them to be reused if we run out of sockets
# Also increase the max packet backlog
net.core.somaxconn = 1024
net.core.netdev_max_backlog = 250000
net.ipv4.tcp_max_syn_backlog = 30000
net.ipv4.tcp_max_tw_buckets = 2000000
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_fin_timeout = 10

# Disable TCP slow start on idle connections
net.ipv4.tcp_slow_start_after_idle = 0

# If your servers talk UDP, also up these limits
net.ipv4.udp_rmem_min = 8192
net.ipv4.udp_wmem_min = 8192

# Disable source routing and redirects
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.all.accept_source_route = 0

# Mellanox recommended changes
net.ipv4.tcp_timestamps = 0
net.ipv4.tcp_sack = 1
net.ipv4.tcp_low_latency = 1
net.ipv4.tcp_adv_win_scale = 1

Jake, thanks for your suggestions.

Andrei
From: "Jake Young" <jak3kaj@xxxxxxxxx>
To: "Andrei Mikhailovsky" <andrei@xxxxxxxxxx>, ceph-users@xxxxxxxxxxxxxx
Sent: Saturday, 6 December, 2014 5:02:15 PM
Subject: Re:  Giant osd problems - loss of IO

Forgot to copy the list. 

I basically cobbled together the settings from examples on the internet.
I basically modified this sysctl.conf file with his suggestion for 10gb nics
http://www.nateware.com/linux-network-tuning-for-2013.html#.VIG_44eLTII

I found these sites helpful as well:

http://fasterdata.es.net/host-tuning/linux/

This may be of interest to you, it has suggestions for your Mellanox hardware: https://fasterdata.es.net/host-tuning/nic-tuning/mellanox-connectx-3/

Fermilab website, link to university research papaer
https://indico.fnal.gov/getFile.py/access?contribId=30&sessionId=19&resId=0&materialId=paper&confId=3377

This has a great answer that explains different configurations for servers vs clients.  It seems to me that osds are both servers and clients, so maybe some of the client tuning would benefit osds as well.  This is where I got the somaxconn setting from.
http://stackoverflow.com/questions/410616/increasing-the-maximum-number-of-tcp-ip-connections-in-linux

I forgot to mention, I'm also setting the txqueuelen for my ceph public nic and ceph private nic in the /etc/rc.local file:
/sbin/ifconfig eth0 txqueuelen 10000
/sbin/ifconfig eth1 txqueuelen 10000

I do push the same sysctl.conf and rc.local to all of my clients as well.  The clients are iSCSI servers which serve vmware hosts.  My ceph cluster is rbd only and I currently only have the iSCSI proxy server clients.  We'll be adding some KVM hypervisors soon, I'm interested to see how they perform vs my vmware --> iSCSI Server --> Ceph setup.

Regarding your sysctl.conf file:

I've read on a few different sites that net.ipv4.tcp_mem should not be tuned, since the defaults are good.  I have not set it, and I can't speak to the benefit/problems with setting it.

You're configured to only use a 4MB TCP buffer, which is very small.  It is actually smaller than the defaults for tcp_wmem, which is 6MB.  The link above suggests up to a 128MB TCP buffer for the 40gb Mellanox and/or 10gb over a WAN (not sure how to read that).  I'm using a 54MB buffer, but I may increase mine to 128MB to see if there is any benefit.  That 4MB buffer may be your problem.

Your net.core.netdev_max_backlog is 5x bigger than mine.  I think I'll increase my setting to 250000 as well.

Our issue looks like http://tracker.ceph.com/issues/9844 and my crash looks like http://tracker.ceph.com/issues/9788

On Fri, Dec 5, 2014 at 5:35 AM, Andrei Mikhailovsky <andrei@xxxxxxxxxx> wrote:
Jake,

very usefull indeed. 

It looks like I had a similar problem regarding the heartbeat and as you' have mentioned, I've not seen such issues on Firefly. However, i've not seen any osd crashes.

Could you please let me know where you got the sysctrl.conf tunings from? Was it recommended by the network vendor?

Also, did you make similar sysctrl.conf changes to your host servers?

A while ago i've read the tunning guide for IP over Infiniband and the Mellanox recommends setting something like this:

net.ipv4.tcp_timestamps = 0
net.ipv4.tcp_sack = 1
net.core.netdev_max_backlog = 250000
net.core.rmem_max = 4194304
net.core.wmem_max = 4194304
net.core.rmem_default = 4194304
net.core.wmem_default = 4194304
net.core.optmem_max = 4194304
net.ipv4.tcp_rmem = 4096 87380 4194304
net.ipv4.tcp_wmem = 4096 65536 4194304
net.ipv4.tcp_mem =4194304 4194304 4194304
net.ipv4.tcp_low_latency=1

which is what I have. Not sure if these are optimal.

I can see that the values are pretty conservative compare to yours. I guess my values should be different as I am running a 40gbit/s network with ipoib. The actual throughput on ipoib is about 20gbit/s according iperf and alike.

Andrei

From: "Jake Young" <jak3kaj@xxxxxxxxx>
To: "Andrei Mikhailovsky" <andrei@xxxxxxxxxx>
Cc: ceph-users@xxxxxxxxxxxxxx
Sent: Thursday, 4 December, 2014 4:57:47 PM
Subject: Re: [ceph-users] Giant osd problems - loss of IO

On Fri, Nov 14, 2014 at 4:38 PM, Andrei Mikhailovsky <andrei@xxxxxxxxxx> wrote:
>
> Any other suggestions why several osds are going down on Giant and causing IO to stall? This was not happening on Firefly.
>
> Thanks
>
>

I had a very similar probem to yours which started after upgrading from Firefly to Giant and then later  I added two new osd nodes, with 7 osds on each. 
My cluster originally had 4 nodes, with 7 osds on each node, 28 osds total, running Gian.  I did not have any problems at this time.  

My problems started after adding two new nodes, so I had 6 nodes and 42 total osds.  It would run fine on low load, but when the request load increased, osds started to fall over.

I was able to set the debug_ms to 10 and capture the logs from a failed OSD.  There were a few different reasons the osds were going down.  This example shows it terminating normally for an unspecified reason a minute after it notices it is marked down in the map.
Osd 25 actually marks this osd (osd 35) down.  For some reason many osds cannot communicate with each other.

There are other examples where I see the "heartbeat_check: no reply from osd.blah" message for long periods of time (hours) and neither osd crashes or terminates.

2014-12-01 16:27:06.772616 7f8b642d1700 -1 osd.35 79679 heartbeat_check: no reply from osd.25 since back 2014-12-01 16:25:51.310319 front 2014-12-01 16:27:06.056972 (cutoff 2014-12-01 16:26:46.772608)
2014-12-01 16:27:07.772767 7f8b642d1700 -1 osd.35 79679 heartbeat_check: no reply from osd.25 since back 2014-12-01 16:25:51.310319 front 2014-12-01 16:27:06.056972 (cutoff 2014-12-01 16:26:47.772759)
2014-12-01 16:27:08.772990 7f8b642d1700 -1 osd.35 79679 heartbeat_check: no reply from osd.25 since back 2014-12-01 16:25:51.310319 front 2014-12-01 16:27:06.056972 (cutoff 2014-12-01 16:26:48.772982)
2014-12-01 16:27:09.559894 7f8b3b1fe700 -1 osd.35 79679 heartbeat_check: no reply from osd.25 since back 2014-12-01 16:25:51.310319 front 2014-12-01 16:27:06.056972 (cutoff 2014-12-01 16:26:49.559891)
2014-12-01 16:27:09.773177 7f8b642d1700 -1 osd.35 79679 heartbeat_check: no reply from osd.25 since back 2014-12-01 16:25:51.310319 front 2014-12-01 16:27:09.559087 (cutoff 2014-12-01 16:26:49.773173)
2014-12-01 16:27:10.773307 7f8b642d1700 -1 osd.35 79679 heartbeat_check: no reply from osd.25 since back 2014-12-01 16:25:51.310319 front 2014-12-01 16:27:09.559087 (cutoff 2014-12-01 16:26:50.773299)
2014-12-01 16:27:11.261557 7f8b3b1fe700 -1 osd.35 79679 heartbeat_check: no reply from osd.25 since back 2014-12-01 16:25:51.310319 front 2014-12-01 16:27:09.559087 (cutoff 2014-12-01 16:26:51.261554)
2014-12-01 16:27:11.773512 7f8b642d1700 -1 osd.35 79679 heartbeat_check: no reply from osd.25 since back 2014-12-01 16:25:51.310319 front 2014-12-01 16:27:11.260129 (cutoff 2014-12-01 16:26:51.773504)
2014-12-01 16:27:12.773741 7f8b642d1700 -1 osd.35 79679 heartbeat_check: no reply from osd.25 since back 2014-12-01 16:25:51.310319 front 2014-12-01 16:27:11.260129 (cutoff 2014-12-01 16:26:52.773733)
2014-12-01 16:27:13.773884 7f8b642d1700 -1 osd.35 79679 heartbeat_check: no reply from osd.25 since back 2014-12-01 16:25:51.310319 front 2014-12-01 16:27:11.260129 (cutoff 2014-12-01 16:26:53.773876)
2014-12-01 16:27:14.163369 7f8b3b1fe700 -1 osd.35 79679 heartbeat_check: no reply from osd.25 since back 2014-12-01 16:25:51.310319 front 2014-12-01 16:27:11.260129 (cutoff 2014-12-01 16:26:54.163366)
2014-12-01 16:27:14.507632 7f8b4fb7f700  0 -- 172.1.2.6:6802/5210 >> 172.1.2.5:6802/2755 pipe(0x2af06940 sd=57 :51521 s=2 pgs=384 cs=1 l=0 c=0x2af094a0).fault with nothing to send, going to standby
2014-12-01 16:27:14.511704 7f8b37af1700  0 -- 172.1.2.6:6802/5210 >> 172.1.2.2:6812/34015988 pipe(0x2af06c00 sd=69 :41512 s=2 pgs=38842 cs=1 l=0 c=0x2af09600).fault with nothing to send, going to standby
2014-12-01 16:27:14.511966 7f8b5030c700  0 -- 172.1.2.6:6802/5210 >> 172.1.2.4:6802/40022302 pipe(0x30cbcdc0 sd=93 :6802 s=2 pgs=66722 cs=3 l=0 c=0x2af091e0).fault with nothing to send, going to standby
2014-12-01 16:27:14.514744 7f8b548a5700  0 -- 172.1.2.6:6802/5210 >> 172.1.2.2:6800/9016639 pipe(0x2af04dc0 sd=38 :60965 s=2 pgs=11747 cs=1 l=0 c=0x2af086e0).fault with nothing to send, going to standby
2014-12-01 16:27:14.516712 7f8b349c7700  0 -- 172.1.2.6:6802/5210 >> 172.1.2.2:6802/25277 pipe(0x2b04cc00 sd=166 :6802 s=2 pgs=62 cs=1 l=0 c=0x2b043080).fault with nothing to send, going to standby
2014-12-01 16:27:14.516814 7f8b2bd3b700  0 -- 172.1.2.6:6802/5210 >> 172.1.2.4:6804/16770 pipe(0x30cbd600 sd=79 :6802 s=2 pgs=607 cs=3 l=0 c=0x2af08c60).fault with nothing to send, going to standby
2014-12-01 16:27:14.518439 7f8b2a422700  0 -- 172.1.2.6:6802/5210 >> 172.1.2.5:6806/31172 pipe(0x30cbc840 sd=28 :6802 s=2 pgs=22 cs=1 l=0 c=0x3041f5a0).fault with nothing to send, going to standby
2014-12-01 16:27:14.518883 7f8b589ba700  0 -- 172.1.2.6:6802/5210 >> 172.1.2.1:6803/4031631 pipe(0x2af042c0 sd=32 :58296 s=2 pgs=35500 cs=3 l=0 c=0x2af08160).fault with nothing to send, going to standby
2014-12-01 16:27:14.519271 7f8b5040d700  0 -- 172.1.2.6:6802/5210 >> 172.1.2.2:6816/32028847 pipe(0x2af05e40 sd=49 :54016 s=2 pgs=30500 cs=1 l=0 c=0x2af08f20).fault with nothing to send, going to standby
2014-12-01 16:27:14.774081 7f8b642d1700 -1 osd.35 79679 heartbeat_check: no reply from osd.25 since back 2014-12-01 16:25:51.310319 front 2014-12-01 16:27:14.161820 (cutoff 2014-12-01 16:26:54.774073)
2014-12-01 16:27:15.774290 7f8b642d1700 -1 osd.35 79679 heartbeat_check: no reply from osd.25 since back 2014-12-01 16:25:51.310319 front 2014-12-01 16:27:14.161820 (cutoff 2014-12-01 16:26:55.774281)
2014-12-01 16:27:16.774480 7f8b642d1700 -1 osd.35 79679 heartbeat_check: no reply from osd.25 since back 2014-12-01 16:25:51.310319 front 2014-12-01 16:27:14.161820 (cutoff 2014-12-01 16:26:56.774471)
2014-12-01 16:27:17.774670 7f8b642d1700 -1 osd.35 79679 heartbeat_check: no reply from osd.25 since back 2014-12-01 16:25:51.310319 front 2014-12-01 16:27:14.161820 (cutoff 2014-12-01 16:26:57.774661)
2014-12-01 16:27:18.264884 7f8b3b1fe700 -1 osd.35 79679 heartbeat_check: no reply from osd.25 since back 2014-12-01 16:25:51.310319 front 2014-12-01 16:27:14.161820 (cutoff 2014-12-01 16:26:58.264882)
2014-12-01 16:27:18.268852 7f8b4c220700  0 log_channel(default) log [WRN] : map e79681 wrongly marked me down
2014-12-01 16:27:22.290362 7f8b37df4700  0 -- 172.1.2.6:6806/1005210 >> 172.1.2.4:6804/16770 pipe(0x2c2ef8c0 sd=75 :44216 s=2 pgs=632 cs=1 l=0 c=0x1bce6940).fault with nothing to send, going to standby
2014-12-01 16:27:22.866677 7f8b56662700  0 -- 172.1.2.6:6806/1005210 >> 172.1.2.2:6808/9013936 pipe(0x2f5e4840 sd=55 :41925 s=2 pgs=15111 cs=1 l=0 c=0x30828580).fault with nothing to send, going to stan
dby
2014-12-01 16:27:24.854642 7f8b2ed6b700  0 -- 172.1.2.6:6806/1005210 >> 172.1.2.6:6816/62000664 pipe(0x2c3c78c0 sd=206 :6806 s=0 pgs=0 cs=0 l=0 c=0x2ccb3e40).accept connect_seq 0 vs existing 0 state con
necting
2014-12-01 16:27:25.265306 7f8b2af2d700  0 -- 172.1.1.6:6806/5210 >> 172.1.1.54:0/586219983 pipe(0x2d46bc80 sd=246 :6806 s=0 pgs=0 cs=0 l=0 c=0x1bdacdc0).accept peer addr is really 172.1.1.54:0/58621998
3 (socket is 172.1.1.54:36423/0)
2014-12-01 16:28:45.732468 7f8b368df700 -1 osd.35 79691 *** Got signal Terminated ***
2014-12-01 16:28:45.732591 7f8b368df700  0 osd.35 79691 prepare_to_stop telling mon we are shutting down
2014-12-01 16:28:46.586316 7f8b2236a700  0 -- 172.1.2.6:6806/1005210 >> 172.1.2.1:6807/91014386 pipe(0x1cabb700 sd=32 :53651 s=2 pgs=37459 cs=1 l=0 c=0x1bce5e40).fault with nothing to send, going to sta
ndby
2014-12-01 16:28:46.593615 7f8b4c220700  0 osd.35 79691 got_stop_ack starting shutdown
2014-12-01 16:28:46.593662 7f8b368df700  0 osd.35 79691 prepare_to_stop starting shutdown
2014-12-01 16:28:46.593682 7f8b368df700 -1 osd.35 79691 shutdown

Another example I found shows this same osd crashing with "hit suicide timeout".  

    -4> 2014-12-01 15:50:52.333350 7fecda368700 10 -- 172.1.2.6:6805/1031451 >> 172.1.2.1:0/32541 pipe(0x2b70a680 sd=104 :6805 s=2 pgs=2692 cs=1 l=1 c=0x2d754680).writer: state = open policy.server=1
    -3> 2014-12-01 15:50:52.333348 7fecd9d62700 10 -- 172.1.1.6:6819/1031451 >> 172.1.2.1:0/32541 pipe(0x4065c80 sd=94 :6819 s=2 pgs=2689 cs=1 l=1 c=0x2d7538c0).writer: state = open policy.server=1
    -2> 2014-12-01 15:50:52.333369 7fecd9d62700 10 -- 172.1.1.6:6819/1031451 >> 172.1.2.1:0/32541 pipe(0x4065c80 sd=94 :6819 s=2 pgs=2689 cs=1 l=1 c=0x2d7538c0).write_ack 10
    -1> 2014-12-01 15:50:52.333386 7fecd9d62700 10 -- 172.1.1.6:6819/1031451 >> 172.1.2.1:0/32541 pipe(0x4065c80 sd=94 :6819 s=2 pgs=2689 cs=1 l=1 c=0x2d7538c0).writer: state = open policy.server=1
     0> 2014-12-01 15:50:52.531714 7fed13221700 -1 common/HeartbeatMap.cc: In function 'bool ceph::HeartbeatMap::_check(ceph::heartbeat_handle_d*, const char*, time_t)' thread 7fed13221700 time 2014-12-
01 15:50:52.508265
common/HeartbeatMap.cc: 79: FAILED assert(0 == "hit suicide timeout")

 ceph version 0.87 (c51c8f9d80fa4e0168aa52685b8de40e42758578)
 1: (ceph::__ceph_assert_fail(char const*, char const*, int, char const*)+0x8b) [0xb8231b]
 2: (ceph::HeartbeatMap::_check(ceph::heartbeat_handle_d*, char const*, long)+0x2a9) [0xac0e19]
 3: (ceph::HeartbeatMap::is_healthy()+0xd6) [0xac16a6]
 4: (ceph::HeartbeatMap::check_touch_file()+0x17) [0xac1d87]
 5: (CephContextServiceThread::entry()+0x154) [0xb96844]
 6: (()+0x8182) [0x7fed175c7182]
 7: (clone()+0x6d) [0x7fed15b31fbd]
 NOTE: a copy of the executable, or `objdump -rdS <executable>` is needed to interpret this.

--- logging levels ---
   0/ 5 none
   0/ 0 lockdep
   0/ 0 context
   0/ 0 crush
   1/ 5 mds
   1/ 5 mds_balancer
   1/ 5 mds_locker
   1/ 5 mds_log
   1/ 5 mds_log_expire
   1/ 5 mds_migrator
   0/ 0 buffer
   0/ 0 timer
   0/ 1 filer
   0/ 1 striper
   0/ 1 objecter
   0/ 5 rados
   0/ 5 rbd
   0/ 5 rbd_replay
   0/ 0 journaler
   0/ 5 objectcacher
   0/ 5 client
   0/ 0 osd
   0/ 0 optracker
   0/ 0 objclass
   0/ 0 filestore
   1/ 3 keyvaluestore
   0/ 0 journal 
10/10 ms
   1/ 5 mon
   0/ 0 monc
   1/ 5 paxos
   0/ 0 tp
   0/ 0 auth
   1/ 5 crypto
   0/ 0 finisher
   0/ 0 heartbeatmap
   0/ 0 perfcounter
   1/ 5 rgw
   1/10 civetweb
   1/ 5 javaclient
   0/ 0 asok
   0/ 0 throttle
   0/ 0 refs
  -2/-2 (syslog threshold)
  -1/-1 (stderr threshold)
  max_recent     10000
  max_new         1000
  log_file /var/log/ceph/ceph-osd.35.log
--- end dump of recent events ---
2014-12-01 15:50:52.627789 7fed13221700 -1 *** Caught signal (Aborted) **
 in thread 7fed13221700

 ceph version 0.87 (c51c8f9d80fa4e0168aa52685b8de40e42758578)
 1: /usr/bin/ceph-osd() [0xa9767a]
 2: (()+0x10340) [0x7fed175cf340]
 3: (gsignal()+0x39) [0x7fed15a6dbb9]
 4: (abort()+0x148) [0x7fed15a70fc8]
 5: (__gnu_cxx::__verbose_terminate_handler()+0x155) [0x7fed163796b5]
 6: (()+0x5e836) [0x7fed16377836]
 7: (()+0x5e863) [0x7fed16377863]
 8: (()+0x5eaa2) [0x7fed16377aa2]
 9: (ceph::__ceph_assert_fail(char const*, char const*, int, char const*)+0x278) [0xb82508]
 10: (ceph::HeartbeatMap::_check(ceph::heartbeat_handle_d*, char const*, long)+0x2a9) [0xac0e19]
 11: (ceph::HeartbeatMap::is_healthy()+0xd6) [0xac16a6]
 12: (ceph::HeartbeatMap::check_touch_file()+0x17) [0xac1d87]
 13: (CephContextServiceThread::entry()+0x154) [0xb96844]
 14: (()+0x8182) [0x7fed175c7182]
 15: (clone()+0x6d) [0x7fed15b31fbd]
 NOTE: a copy of the executable, or `objdump -rdS <executable>` is needed to interpret this.

--- logging levels ---
   0/ 5 none
   0/ 0 lockdep
   0/ 0 context
   0/ 0 crush
   1/ 5 mds
   1/ 5 mds_balancer
   1/ 5 mds_locker
   1/ 5 mds_log
   1/ 5 mds_log_expire
   1/ 5 mds_migrator
   0/ 0 buffer
   0/ 0 timer
   0/ 1 filer
   0/ 1 striper
   0/ 1 objecter
   0/ 5 rados
   0/ 5 rbd
   0/ 5 rbd_replay
   0/ 0 journaler
   0/ 5 objectcacher
   0/ 5 client
   0/ 0 osd
   0/ 0 optracker
   0/ 0 objclass
   0/ 0 filestore
   1/ 3 keyvaluestore
   0/ 0 journal
  10/10 ms
   1/ 5 mon
   0/ 0 monc
   1/ 5 paxos
   0/ 0 tp
   0/ 0 auth
   1/ 5 crypto
   0/ 0 finisher
   0/ 0 heartbeatmap
   0/ 0 perfcounter
   1/ 5 rgw
   1/10 civetweb
   1/ 5 javaclient
   0/ 0 asok
   0/ 0 throttle
   0/ 0 refs
  -2/-2 (syslog threshold)
  -1/-1 (stderr threshold)
  max_recent     10000
  max_new         1000
  log_file /var/log/ceph/ceph-osd.35.log
--- end dump of recent events ---

The recurring theme here is that there is a communication issue between the osds.  

I looked carefully at my network hardware configuration (UCS C240s with 40Gbps Cisco VICs connected to a pair of Nexus 5672 using A-FEX Port Profile configuration) and couldn't find any dropped packets or errors.

I ran "ss -s" for the first time on my osds and was a bit suprised to see how many open TCP connections they all have.  

ceph@osd6:/var/log/ceph$ ss -s
Total: 1492 (kernel 0)
TCP:   1411 (estab 1334, closed 40, orphaned 0, synrecv 0, timewait 0/0), ports 0

Transport Total     IP        IPv6
*	  0         -         -
RAW	  0         0         0
UDP	  10        4         6
TCP	  1371      1369      2
INET	  1381      1373      8
FRAG	  0         0         0

While researching if additional kernel tuning would be required to handle so many connections, I eventually realized that I forgot to copy my customized /etc/sysctl.conf file on the two new nodes. I'm not sure if the large amount of TCP connections is part of the performance enhancements between Giant and Firefly, or if Firefly uses a similar number of connections.

I highlighted the tuning parameters that I suspect are required. 

ceph@osd6:/var/log/ceph$ cat /etc/sysctl.conf
#
# /etc/sysctl.conf - Configuration file for setting system variables
# See /etc/sysctl.d/ for additional system variables
# See sysctl.conf (5) for information.
#

# Increase Linux autotuning TCP buffer limits
# Set max to 16MB for 1GE and 32M (33554432) or 54M (56623104) for 10GE
# Don't set tcp_mem itself! Let the kernel scale it based on RAM.
net.core.rmem_max = 56623104
net.core.wmem_max = 56623104
net.core.rmem_default = 56623104
net.core.wmem_default = 56623104
net.core.optmem_max = 40960
net.ipv4.tcp_rmem = 4096 87380 56623104
net.ipv4.tcp_wmem = 4096 65536 56623104

# Make room for more TIME_WAIT sockets due to more clients,
# and allow them to be reused if we run out of sockets
# Also increase the max packet backlog
net.core.somaxconn = 1024
net.core.netdev_max_backlog = 50000
net.ipv4.tcp_max_syn_backlog = 30000
net.ipv4.tcp_max_tw_buckets = 2000000
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_fin_timeout = 10

# Disable TCP slow start on idle connections
net.ipv4.tcp_slow_start_after_idle = 0

# If your servers talk UDP, also up these limits
net.ipv4.udp_rmem_min = 8192
net.ipv4.udp_wmem_min = 8192

# Disable source routing and redirects
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.all.accept_source_route = 0

I added the net.core.somaxconn after this experience, since the default is 128.  This represents the allowed socket backlog in the kernel; which should help when I reboot an osd node and 1300 connections need to be made quickly.

I found that I needed to restart my osds after applying the kernel tuning above for my cluster to stabilize.

My system is now stable again and performs very well.

I hope this helps someone out.  It took me a few days of troubleshooting to get to the bottom of this.

Jake

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