We had multiple issues with 4TB drives and delays. Here is the configuration that works for us fairly well on Ubuntu (but we are about to significantly increase the IO load so this may change).
GRUB_CMDLINE_LINUX_DEFAULT="elevator=noop nomodeset splash=silent vga=normal net.ifnames=0 biosdevname=0 scsi_mod.use_blk_mq=Y"
blk_mq really helps with spreading the IO load over multiple cores.
chmod -x /etc/init.d/ondemand - in order to prevent CPU throttling
vm.swappiness=1
vm.min_free_kbytes=1048576
NTP: always use NTP and make sure it is working - Ceph is very sensitive to time being precise
/etc/default/grub:
GRUB_CMDLINE_LINUX_DEFAULT="elevator=noop nomodeset splash=silent vga=normal net.ifnames=0 biosdevname=0 scsi_mod.use_blk_mq=Y"
blk_mq really helps with spreading the IO load over multiple cores.
I used to use intel_idle.max_cstate=0 processor.max_cstate=0 idle=poll, but it seems allowing idle states actually can improve performance by running CPUs cooler, so will likely remove this soon.
use Mellanox OFED on pre-4.x kernels
check your flow control settings on server and switch using ethtool
test network performance with iperf
disable firewall rules or just uninstall firewall (e.g. ufw)
Turn off in BIOS any virtualization technology VT-d etc., and (see note above re C-states) maybe also disable power saving features
/etc/sysctl.conf:
kernel.pid_max = 4194303vm.swappiness=1
vm.min_free_kbytes=1048576
Hope this helps.
Alex
On Sun, Oct 4, 2015 at 2:16 AM, Josef Johansson <josef86@xxxxxxxxx> wrote:
Hi,
I don't know what brand those 4TB spindles are, but I know that mine are very bad at doing write at the same time as read. Especially small read write.
This has an absurdly bad effect when doing maintenance on ceph. That being said we see a lot of difference between dumpling and hammer in performance on these drives. Most likely due to hammer able to read write degraded PGs.
We have run into two different problems along the way, the first was blocked request where we had to upgrade from 64GB mem on each node to 256GB. We thought that it was the only safe buy make things better.
I believe it worked because more reads were cached so we had less mixed read write on the nodes, thus giving the spindles more room to breath. Now this was a shot in the dark then, but the price is not that high even to just try it out.. compared to 6 people working on it. I believe the IO on disk was not huge either, but what kills the disk is high latency. How much bandwidth are the disk using? We had very low.. 3-5MB/s.
The second problem was defragmentations hitting 70%, lowering that to 6% made a lot of difference. Depending on IO pattern this increases different.
TL;DR read kills the 4TB spindles.
Hope you guys clear out of the woods.
/JosefOn 3 Oct 2015 10:10 pm, "Robert LeBlanc" <robert@xxxxxxxxxxxxx> wrote:-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256
We are still struggling with this and have tried a lot of different
things. Unfortunately, Inktank (now Red Hat) no longer provides
consulting services for non-Red Hat systems. If there are some
certified Ceph consultants in the US that we can do both remote and
on-site engagements, please let us know.
This certainly seems to be network related, but somewhere in the
kernel. We have tried increasing the network and TCP buffers, number
of TCP sockets, reduced the FIN_WAIT2 state. There is about 25% idle
on the boxes, the disks are busy, but not constantly at 100% (they
cycle from <10% up to 100%, but not 100% for more than a few seconds
at a time). There seems to be no reasonable explanation why I/O is
blocked pretty frequently longer than 30 seconds. We have verified
Jumbo frames by pinging from/to each node with 9000 byte packets. The
network admins have verified that packets are not being dropped in the
switches for these nodes. We have tried different kernels including
the recent Google patch to cubic. This is showing up on three cluster
(two Ethernet and one IPoIB). I booted one cluster into Debian Jessie
(from CentOS 7.1) with similar results.
The messages seem slightly different:
2015-10-03 14:38:23.193082 osd.134 10.208.16.25:6800/1425 439 :
cluster [WRN] 14 slow requests, 1 included below; oldest blocked for >
100.087155 secs
2015-10-03 14:38:23.193090 osd.134 10.208.16.25:6800/1425 440 :
cluster [WRN] slow request 30.041999 seconds old, received at
2015-10-03 14:37:53.151014: osd_op(client.1328605.0:7082862
rbd_data.13fdcb2ae8944a.000000000001264f [read 975360~4096]
11.6d19c36f ack+read+known_if_redirected e10249) currently no flag
points reached
I don't know what "no flag points reached" means.
The problem is most pronounced when we have to reboot an OSD node (1
of 13), we will have hundreds of I/O blocked for some times up to 300
seconds. It takes a good 15 minutes for things to settle down. The
production cluster is very busy doing normally 8,000 I/O and peaking
at 15,000. This is all 4TB spindles with SSD journals and the disks
are between 25-50% full. We are currently splitting PGs to distribute
the load better across the disks, but we are having to do this 10 PGs
at a time as we get blocked I/O. We have max_backfills and
max_recovery set to 1, client op priority is set higher than recovery
priority. We tried increasing the number of op threads but this didn't
seem to help. It seems as soon as PGs are finished being checked, they
become active and could be the cause for slow I/O while the other PGs
are being checked.
What I don't understand is that the messages are delayed. As soon as
the message is received by Ceph OSD process, it is very quickly
committed to the journal and a response is sent back to the primary
OSD which is received very quickly as well. I've adjust
min_free_kbytes and it seems to keep the OSDs from crashing, but
doesn't solve the main problem. We don't have swap and there is 64 GB
of RAM per nodes for 10 OSDs.
Is there something that could cause the kernel to get a packet but not
be able to dispatch it to Ceph such that it could be explaining why we
are seeing these blocked I/O for 30+ seconds. Is there some pointers
to tracing Ceph messages from the network buffer through the kernel to
the Ceph process?
We can really use some pointers no matter how outrageous. We've have
over 6 people looking into this for weeks now and just can't think of
anything else.
Thanks,
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----------------
Robert LeBlanc
PGP Fingerprint 79A2 9CA4 6CC4 45DD A904 C70E E654 3BB2 FA62 B9F1
On Fri, Sep 25, 2015 at 2:40 PM, Robert LeBlanc <robert@xxxxxxxxxxxxx> wrote:
> We dropped the replication on our cluster from 4 to 3 and it looks
> like all the blocked I/O has stopped (no entries in the log for the
> last 12 hours). This makes me believe that there is some issue with
> the number of sockets or some other TCP issue. We have not messed with
> Ephemeral ports and TIME_WAIT at this point. There are 130 OSDs, 8 KVM
> hosts hosting about 150 VMs. Open files is set at 32K for the OSD
> processes and 16K system wide.
>
> Does this seem like the right spot to be looking? What are some
> configuration items we should be looking at?
>
> Thanks,
> ----------------
> Robert LeBlanc
> PGP Fingerprint 79A2 9CA4 6CC4 45DD A904 C70E E654 3BB2 FA62 B9F1
>
>
> On Wed, Sep 23, 2015 at 1:30 PM, Robert LeBlanc <robert@xxxxxxxxxxxxx> wrote:
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA256
>>
>> We were able to only get ~17Gb out of the XL710 (heavily tweaked)
>> until we went to the 4.x kernel where we got ~36Gb (no tweaking). It
>> seems that there were some major reworks in the network handling in
>> the kernel to efficiently handle that network rate. If I remember
>> right we also saw a drop in CPU utilization. I'm starting to think
>> that we did see packet loss while congesting our ISLs in our initial
>> testing, but we could not tell where the dropping was happening. We
>> saw some on the switches, but it didn't seem to be bad if we weren't
>> trying to congest things. We probably already saw this issue, just
>> didn't know it.
>> - ----------------
>> Robert LeBlanc
>> PGP Fingerprint 79A2 9CA4 6CC4 45DD A904 C70E E654 3BB2 FA62 B9F1
>>
>>
>> On Wed, Sep 23, 2015 at 1:10 PM, Mark Nelson wrote:
>>> FWIW, we've got some 40GbE Intel cards in the community performance cluster
>>> on a Mellanox 40GbE switch that appear (knock on wood) to be running fine
>>> with 3.10.0-229.7.2.el7.x86_64. We did get feedback from Intel that older
>>> drivers might cause problems though.
>>>
>>> Here's ifconfig from one of the nodes:
>>>
>>> ens513f1: flags=4163 mtu 1500
>>> inet 10.0.10.101 netmask 255.255.255.0 broadcast 10.0.10.255
>>> inet6 fe80::6a05:caff:fe2b:7ea1 prefixlen 64 scopeid 0x20
>>> ether 68:05:ca:2b:7e:a1 txqueuelen 1000 (Ethernet)
>>> RX packets 169232242875 bytes 229346261232279 (208.5 TiB)
>>> RX errors 0 dropped 0 overruns 0 frame 0
>>> TX packets 153491686361 bytes 203976410836881 (185.5 TiB)
>>> TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
>>>
>>> Mark
>>>
>>>
>>> On 09/23/2015 01:48 PM, Robert LeBlanc wrote:
>>>>
>>>> -----BEGIN PGP SIGNED MESSAGE-----
>>>> Hash: SHA256
>>>>
>>>> OK, here is the update on the saga...
>>>>
>>>> I traced some more of blocked I/Os and it seems that communication
>>>> between two hosts seemed worse than others. I did a two way ping flood
>>>> between the two hosts using max packet sizes (1500). After 1.5M
>>>> packets, no lost pings. Then then had the ping flood running while I
>>>> put Ceph load on the cluster and the dropped pings started increasing
>>>> after stopping the Ceph workload the pings stopped dropping.
>>>>
>>>> I then ran iperf between all the nodes with the same results, so that
>>>> ruled out Ceph to a large degree. I then booted in the the
>>>> 3.10.0-229.14.1.el7.x86_64 kernel and with an hour test so far there
>>>> hasn't been any dropped pings or blocked I/O. Our 40 Gb NICs really
>>>> need the network enhancements in the 4.x series to work well.
>>>>
>>>> Does this sound familiar to anyone? I'll probably start bisecting the
>>>> kernel to see where this issue in introduced. Both of the clusters
>>>> with this issue are running 4.x, other than that, they are pretty
>>>> differing hardware and network configs.
>>>>
>>>> Thanks,
>>>> -----BEGIN PGP SIGNATURE-----
>>>> Version: Mailvelope v1.1.0
>>>> Comment: https://www.mailvelope.com
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>>>> =P33I
>>>> -----END PGP SIGNATURE-----
>>>> ----------------
>>>> Robert LeBlanc
>>>> PGP Fingerprint 79A2 9CA4 6CC4 45DD A904 C70E E654 3BB2 FA62 B9F1
>>>>
>>>>
>>>> On Tue, Sep 22, 2015 at 4:15 PM, Robert LeBlanc
>>>> wrote:
>>>>>
>>>>> -----BEGIN PGP SIGNED MESSAGE-----
>>>>> Hash: SHA256
>>>>>
>>>>> This is IPoIB and we have the MTU set to 64K. There was some issues
>>>>> pinging hosts with "No buffer space available" (hosts are currently
>>>>> configured for 4GB to test SSD caching rather than page cache). I
>>>>> found that MTU under 32K worked reliable for ping, but still had the
>>>>> blocked I/O.
>>>>>
>>>>> I reduced the MTU to 1500 and checked pings (OK), but I'm still seeing
>>>>> the blocked I/O.
>>>>> - ----------------
>>>>> Robert LeBlanc
>>>>> PGP Fingerprint 79A2 9CA4 6CC4 45DD A904 C70E E654 3BB2 FA62 B9F1
>>>>>
>>>>>
>>>>> On Tue, Sep 22, 2015 at 3:52 PM, Sage Weil wrote:
>>>>>>
>>>>>> On Tue, 22 Sep 2015, Samuel Just wrote:
>>>>>>>
>>>>>>> I looked at the logs, it looks like there was a 53 second delay
>>>>>>> between when osd.17 started sending the osd_repop message and when
>>>>>>> osd.13 started reading it, which is pretty weird. Sage, didn't we
>>>>>>> once see a kernel issue which caused some messages to be mysteriously
>>>>>>> delayed for many 10s of seconds?
>>>>>>
>>>>>>
>>>>>> Every time we have seen this behavior and diagnosed it in the wild it
>>>>>> has
>>>>>> been a network misconfiguration. Usually related to jumbo frames.
>>>>>>
>>>>>> sage
>>>>>>
>>>>>>
>>>>>>>
>>>>>>> What kernel are you running?
>>>>>>> -Sam
>>>>>>>
>>>>>>> On Tue, Sep 22, 2015 at 2:22 PM, Robert LeBlanc wrote:
>>>>>>>>
>>>>>>>> -----BEGIN PGP SIGNED MESSAGE-----
>>>>>>>> Hash: SHA256
>>>>>>>>
>>>>>>>> OK, looping in ceph-devel to see if I can get some more eyes. I've
>>>>>>>> extracted what I think are important entries from the logs for the
>>>>>>>> first blocked request. NTP is running all the servers so the logs
>>>>>>>> should be close in terms of time. Logs for 12:50 to 13:00 are
>>>>>>>> available at http://162.144.87.113/files/ceph_block_io.logs.tar.xz
>>>>>>>>
>>>>>>>> 2015-09-22 12:55:06.500374 - osd.17 gets I/O from client
>>>>>>>> 2015-09-22 12:55:06.557160 - osd.17 submits I/O to osd.13
>>>>>>>> 2015-09-22 12:55:06.557305 - osd.17 submits I/O to osd.16
>>>>>>>> 2015-09-22 12:55:06.573711 - osd.16 gets I/O from osd.17
>>>>>>>> 2015-09-22 12:55:06.595716 - osd.17 gets ondisk result=0 from osd.16
>>>>>>>> 2015-09-22 12:55:06.640631 - osd.16 reports to osd.17 ondisk result=0
>>>>>>>> 2015-09-22 12:55:36.926691 - osd.17 reports slow I/O > 30.439150 sec
>>>>>>>> 2015-09-22 12:55:59.790591 - osd.13 gets I/O from osd.17
>>>>>>>> 2015-09-22 12:55:59.812405 - osd.17 gets ondisk result=0 from osd.13
>>>>>>>> 2015-09-22 12:56:02.941602 - osd.13 reports to osd.17 ondisk result=0
>>>>>>>>
>>>>>>>> In the logs I can see that osd.17 dispatches the I/O to osd.13 and
>>>>>>>> osd.16 almost silmutaniously. osd.16 seems to get the I/O right away,
>>>>>>>> but for some reason osd.13 doesn't get the message until 53 seconds
>>>>>>>> later. osd.17 seems happy to just wait and doesn't resend the data
>>>>>>>> (well, I'm not 100% sure how to tell which entries are the actual data
>>>>>>>> transfer).
>>>>>>>>
>>>>>>>> It looks like osd.17 is receiving responses to start the communication
>>>>>>>> with osd.13, but the op is not acknowledged until almost a minute
>>>>>>>> later. To me it seems that the message is getting received but not
>>>>>>>> passed to another thread right away or something. This test was done
>>>>>>>> with an idle cluster, a single fio client (rbd engine) with a single
>>>>>>>> thread.
>>>>>>>>
>>>>>>>> The OSD servers are almost 100% idle during these blocked I/O
>>>>>>>> requests. I think I'm at the end of my troubleshooting, so I can use
>>>>>>>> some help.
>>>>>>>>
>>>>>>>> Single Test started about
>>>>>>>> 2015-09-22 12:52:36
>>>>>>>>
>>>>>>>> 2015-09-22 12:55:36.926680 osd.17 192.168.55.14:6800/16726 56 :
>>>>>>>> cluster [WRN] 1 slow requests, 1 included below; oldest blocked for >
>>>>>>>> 30.439150 secs
>>>>>>>> 2015-09-22 12:55:36.926699 osd.17 192.168.55.14:6800/16726 57 :
>>>>>>>> cluster [WRN] slow request 30.439150 seconds old, received at
>>>>>>>> 2015-09-22 12:55:06.487451:
>>>>>>>> osd_op(client.250874.0:1388 rbd_data.3380e2ae8944a.0000000000000545
>>>>>>>> [set-alloc-hint object_size 4194304 write_size 4194304,write
>>>>>>>> 0~4194304] 8.bbf3e8ff ack+ondisk+write+known_if_redirected e56785)
>>>>>>>> currently waiting for subops from 13,16
>>>>>>>> 2015-09-22 12:55:36.697904 osd.16 192.168.55.13:6800/29410 7 : cluster
>>>>>>>> [WRN] 2 slow requests, 2 included below; oldest blocked for >
>>>>>>>> 30.379680 secs
>>>>>>>> 2015-09-22 12:55:36.697918 osd.16 192.168.55.13:6800/29410 8 : cluster
>>>>>>>> [WRN] slow request 30.291520 seconds old, received at 2015-09-22
>>>>>>>> 12:55:06.406303:
>>>>>>>> osd_op(client.250874.0:1384 rbd_data.3380e2ae8944a.0000000000000541
>>>>>>>> [set-alloc-hint object_size 4194304 write_size 4194304,write
>>>>>>>> 0~4194304] 8.5fb2123f ack+ondisk+write+known_if_redirected e56785)
>>>>>>>> currently waiting for subops from 13,17
>>>>>>>> 2015-09-22 12:55:36.697927 osd.16 192.168.55.13:6800/29410 9 : cluster
>>>>>>>> [WRN] slow request 30.379680 seconds old, received at 2015-09-22
>>>>>>>> 12:55:06.318144:
>>>>>>>> osd_op(client.250874.0:1382 rbd_data.3380e2ae8944a.000000000000053f
>>>>>>>> [set-alloc-hint object_size 4194304 write_size 4194304,write
>>>>>>>> 0~4194304] 8.312e69ca ack+ondisk+write+known_if_redirected e56785)
>>>>>>>> currently waiting for subops from 13,14
>>>>>>>> 2015-09-22 12:58:03.998275 osd.13 192.168.55.12:6804/4574 130 :
>>>>>>>> cluster [WRN] 1 slow requests, 1 included below; oldest blocked for >
>>>>>>>> 30.954212 secs
>>>>>>>> 2015-09-22 12:58:03.998286 osd.13 192.168.55.12:6804/4574 131 :
>>>>>>>> cluster [WRN] slow request 30.954212 seconds old, received at
>>>>>>>> 2015-09-22 12:57:33.044003:
>>>>>>>> osd_op(client.250874.0:1873 rbd_data.3380e2ae8944a.000000000000070d
>>>>>>>> [set-alloc-hint object_size 4194304 write_size 4194304,write
>>>>>>>> 0~4194304] 8.e69870d4 ack+ondisk+write+known_if_redirected e56785)
>>>>>>>> currently waiting for subops from 16,17
>>>>>>>> 2015-09-22 12:58:03.759826 osd.16 192.168.55.13:6800/29410 10 :
>>>>>>>> cluster [WRN] 1 slow requests, 1 included below; oldest blocked for >
>>>>>>>> 30.704367 secs
>>>>>>>> 2015-09-22 12:58:03.759840 osd.16 192.168.55.13:6800/29410 11 :
>>>>>>>> cluster [WRN] slow request 30.704367 seconds old, received at
>>>>>>>> 2015-09-22 12:57:33.055404:
>>>>>>>> osd_op(client.250874.0:1874 rbd_data.3380e2ae8944a.000000000000070e
>>>>>>>> [set-alloc-hint object_size 4194304 write_size 4194304,write
>>>>>>>> 0~4194304] 8.f7635819 ack+ondisk+write+known_if_redirected e56785)
>>>>>>>> currently waiting for subops from 13,17
>>>>>>>>
>>>>>>>> Server IP addr OSD
>>>>>>>> nodev - 192.168.55.11 - 12
>>>>>>>> nodew - 192.168.55.12 - 13
>>>>>>>> nodex - 192.168.55.13 - 16
>>>>>>>> nodey - 192.168.55.14 - 17
>>>>>>>> nodez - 192.168.55.15 - 14
>>>>>>>> nodezz - 192.168.55.16 - 15
>>>>>>>>
>>>>>>>> fio job:
>>>>>>>> [rbd-test]
>>>>>>>> readwrite=write
>>>>>>>> blocksize=4M
>>>>>>>> #runtime=60
>>>>>>>> name=rbd-test
>>>>>>>> #readwrite=randwrite
>>>>>>>> #bssplit=4k/85:32k/11:512/3:1m/1,4k/89:32k/10:512k/1
>>>>>>>> #rwmixread=72
>>>>>>>> #norandommap
>>>>>>>> #size=1T
>>>>>>>> #blocksize=4k
>>>>>>>> ioengine=rbd
>>>>>>>> rbdname=test2
>>>>>>>> pool=rbd
>>>>>>>> clientname=admin
>>>>>>>> iodepth=8
>>>>>>>> #numjobs=4
>>>>>>>> #thread
>>>>>>>> #group_reporting
>>>>>>>> #time_based
>>>>>>>> #direct=1
>>>>>>>> #ramp_time=60
>>>>>>>>
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> -----BEGIN PGP SIGNATURE-----
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>>>>>>>> Comment: https://www.mailvelope.com
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>>>>>>>> -----END PGP SIGNATURE-----
>>>>>>>> ----------------
>>>>>>>> Robert LeBlanc
>>>>>>>> PGP Fingerprint 79A2 9CA4 6CC4 45DD A904 C70E E654 3BB2 FA62 B9F1
>>>>>>>>
>>>>>>>>
>>>>>>>> On Tue, Sep 22, 2015 at 8:31 AM, Gregory Farnum wrote:
>>>>>>>>>
>>>>>>>>> On Tue, Sep 22, 2015 at 7:24 AM, Robert LeBlanc wrote:
>>>>>>>>>>
>>>>>>>>>> -----BEGIN PGP SIGNED MESSAGE-----
>>>>>>>>>> Hash: SHA256
>>>>>>>>>>
>>>>>>>>>> Is there some way to tell in the logs that this is happening?
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> You can search for the (mangled) name _split_collection
>>>>>>>>>>
>>>>>>>>>> I'm not
>>>>>>>>>> seeing much I/O, CPU usage during these times. Is there some way to
>>>>>>>>>> prevent the splitting? Is there a negative side effect to doing so?
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Bump up the split and merge thresholds. You can search the list for
>>>>>>>>> this, it was discussed not too long ago.
>>>>>>>>>
>>>>>>>>>> We've had I/O block for over 900 seconds and as soon as the sessions
>>>>>>>>>> are aborted, they are reestablished and complete immediately.
>>>>>>>>>>
>>>>>>>>>> The fio test is just a seq write, starting it over (rewriting from
>>>>>>>>>> the
>>>>>>>>>> beginning) is still causing the issue. I was suspect that it is not
>>>>>>>>>> having to create new file and therefore split collections. This is
>>>>>>>>>> on
>>>>>>>>>> my test cluster with no other load.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Hmm, that does make it seem less likely if you're really not creating
>>>>>>>>> new objects, if you're actually running fio in such a way that it's
>>>>>>>>> not allocating new FS blocks (this is probably hard to set up?).
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> I'll be doing a lot of testing today. Which log options and depths
>>>>>>>>>> would be the most helpful for tracking this issue down?
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> If you want to go log diving "debug osd = 20", "debug filestore =
>>>>>>>>> 20",
>>>>>>>>> "debug ms = 1" are what the OSD guys like to see. That should spit
>>>>>>>>> out
>>>>>>>>> everything you need to track exactly what each Op is doing.
>>>>>>>>> -Greg
>>>>>>>>
>>>>>>>> --
>>>>>>>> To unsubscribe from this list: send the line "unsubscribe ceph-devel"
>>>>>>>> in
>>>>>>>> the body of a message to majordomo@xxxxxxxxxxxxxxx
>>>>>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>
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>>>>
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe ceph-devel" in
>>>> the body of a message to majordomo@xxxxxxxxxxxxxxx
>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>>>>
>>>
>>
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