Re: RBD Read performance

[Malcolm Haak <malcolm@sgi.com>]

Hi all,

We switched to a, now free, Sandy Bridge based server.

This has resolved our read issues. So something about the Quad AMD box 
was very bad for reads...

I've got numbers if people are interested.. but I would say that AMD is 
not a great idea for OSD's.

Thanks for all the pointers!

Regards

Malcolm Haak

On 19/04/13 12:21, Malcolm Haak wrote:
> Ok this is getting interesting.
>
> rados -p <pool> bench 300 write --no-cleanup
>
>   Total time run:         301.103933
> Total writes made:      22477
> Write size:             4194304
> Bandwidth (MB/sec):     298.595
>
> Stddev Bandwidth:       171.941
> Max bandwidth (MB/sec): 832
> Min bandwidth (MB/sec): 8
> Average Latency:        0.214295
> Stddev Latency:         0.405511
> Max latency:            3.26323
> Min latency:            0.019429
>
>
>   rados -p <pool> bench 300 seq
>
>   Total time run:        76.634659
> Total reads made:     22477
> Read size:            4194304
> Bandwidth (MB/sec):    1173.203
>
> Average Latency:       0.054539
> Max latency:           0.937036
> Min latency:           0.018132
>
>
> So the writes on the rados bench are slower than we have achieved with
> dd and were slower on the back-end file store as well. But the reads are
> great. We could see 1~1.5GB/s on the back-end as well.
>
> So we started doing some other tests to see if it was in RBD or the VFS
> layer in the kernel.. And things got weird.
>
> So using CephFS:
>
> root@dogbreath ~]# dd if=/dev/zero of=/test-fs/DELETEME1 bs=1G count=10
> 10+0 records in
> 10+0 records out
> 10737418240 bytes (11 GB) copied, 7.28658 s, 1.5 GB/s
> [root@dogbreath ~]# dd if=/dev/zero of=/test-fs/DELETEME1 bs=1G count=20
> 20+0 records in
> 20+0 records out
> 21474836480 bytes (21 GB) copied, 20.6105 s, 1.0 GB/s
> [root@dogbreath ~]# dd if=/dev/zero of=/test-fs/DELETEME1 bs=1G count=40
> 40+0 records in
> 40+0 records out
> 42949672960 bytes (43 GB) copied, 53.4013 s, 804 MB/s
> [root@dogbreath ~]# dd if=/test-fs/DELETEME1 of=/dev/null bs=1G count=4
> iflag=direct
> 4+0 records in
> 4+0 records out
> 4294967296 bytes (4.3 GB) copied, 23.1572 s, 185 MB/s
> [root@dogbreath ~]#
> [root@dogbreath ~]# dd if=/test-fs/DELETEME1 of=/dev/null bs=1G count=4
> 4+0 records in
> 4+0 records out
> 4294967296 bytes (4.3 GB) copied, 1.20258 s, 3.6 GB/s
> [root@dogbreath ~]# dd if=/test-fs/DELETEME1 of=/dev/null bs=1G count=20
> 20+0 records in
> 20+0 records out
> 21474836480 bytes (21 GB) copied, 5.40589 s, 4.0 GB/s
> [root@dogbreath ~]# dd if=/test-fs/DELETEME1 of=/dev/null bs=1G count=40
> 40+0 records in
> 40+0 records out
> 42949672960 bytes (43 GB) copied, 10.4781 s, 4.1 GB/s
> [root@dogbreath ~]# echo 1 > /proc/sys/vm/drop_caches
> [root@dogbreath ~]# dd if=/test-fs/DELETEME1 of=/dev/null bs=1G count=40
> ^C24+0 records in
> 23+0 records out
> 24696061952 bytes (25 GB) copied, 56.8824 s, 434 MB/s
>
> [root@dogbreath ~]# dd if=/test-fs/DELETEME1 of=/dev/null bs=1G count=40
> 40+0 records in
> 40+0 records out
> 42949672960 bytes (43 GB) copied, 113.542 s, 378 MB/s
> [root@dogbreath ~]#
>
> So about the same, when we were not hitting cache. So we decided to just
> hit the RBD block device with no FS on it.. Welcome to weirdsville
>
> root@ty3:~# umount /test-rbd-fs
> root@ty3:~#
> root@ty3:~# dd if=/dev/rbd1 of=/dev/null bs=1G count=4
> 4+0 records in
> 4+0 records out
> 4294967296 bytes (4.3 GB) copied, 18.6603 s, 230 MB/s
> root@ty3:~# dd if=/dev/rbd1 of=/dev/null bs=1G count=4 iflag=direct
> 4+0 records in
> 4+0 records out
> 4294967296 bytes (4.3 GB) copied, 1.13584 s, 3.8 GB/s
> root@ty3:~# dd if=/dev/rbd1 of=/dev/null bs=1G count=20 iflag=direct
> 20+0 records in
> 20+0 records out
> 21474836480 bytes (21 GB) copied, 4.61028 s, 4.7 GB/s
> root@ty3:~# echo 1 > /proc/sys/vm/drop_caches
> root@ty3:~# dd if=/dev/rbd1 of=/dev/null bs=1G count=20 iflag=direct
> 20+0 records in
> 20+0 records out
> 21474836480 bytes (21 GB) copied, 4.43416 s, 4.8 GB/s
> root@ty3:~# echo 1 > /proc/sys/vm/drop_caches
> root@ty3:~#
> root@ty3:~#
> root@ty3:~# dd if=/dev/rbd1 of=/dev/null bs=1G count=20 iflag=direct
> 20+0 records in
> 20+0 records out
> 21474836480 bytes (21 GB) copied, 5.07426 s, 4.2 GB/s
> root@ty3:~# dd if=/dev/rbd1 of=/dev/null bs=1G count=40 iflag=direct
> 40+0 records in
> 40+0 records out
> 42949672960 bytes (43 GB) copied, 8.60885 s, 5.0 GB/s
> root@ty3:~# dd if=/dev/rbd1 of=/dev/null bs=1G count=80 iflag=direct
> 80+0 records in
> 80+0 records out
> 85899345920 bytes (86 GB) copied, 18.4305 s, 4.7 GB/s
> root@ty3:~# dd if=/dev/rbd1 of=/dev/null bs=1G count=20
> 20+0 records in
> 20+0 records out
> 21474836480 bytes (21 GB) copied, 91.5546 s, 235 MB/s
> root@ty3:~#
>
> So.. we just started reading from the block device. And the numbers were
> well.. Faster than the QDR IB can do TCP/IP. So we figured local
> caching. So we dropped caches and ramped up to bigger than ram. (ram is
> 24GB) and it got faster. So we went to 3x ram.. and it was a bit slower..
>
> Oh also the whole time we were doing these tests, the back-end disk was
> seeing no I/O at all.. We were dropping caches on the OSD's as well, but
> even if it was caching at the OSD end, the IB link is only QDR and we
> aren't doing RDMA so. Yeah..No idea what is going on here...
>
>
> On 19/04/13 10:40, Mark Nelson wrote:
>> On 04/18/2013 07:27 PM, Malcolm Haak wrote:
>>> Morning all,
>>>
>>> Did the echos on all boxes involved... and the results are in..
>>>
>>> [root@dogbreath ~]#
>>> [root@dogbreath ~]# dd if=/test-rbd-fs/DELETEME of=/dev/null bs=4M
>>> count=10000 iflag=direct
>>> 10000+0 records in
>>> 10000+0 records out
>>> 41943040000 bytes (42 GB) copied, 144.083 s, 291 MB/s
>>> [root@dogbreath ~]# dd if=/test-rbd-fs/DELETEME of=/dev/null bs=4M
>>> count=10000
>>> 10000+0 records in
>>> 10000+0 records out
>>> 41943040000 bytes (42 GB) copied, 316.025 s, 133 MB/s
>>> [root@dogbreath ~]#
>>
>> Boo!
>>
>>>
>>> No change which is a shame. What other information or testing should I
>>> start?
>>
>> Any chance you can try out a quick rados bench test from the client
>> against the pool for writes and reads and see how that works?
>>
>> rados -p <pool> bench 300 write --no-cleanup
>> rados -p <pool> bench 300 seq
>>
>>>
>>> Regards
>>>
>>> Malcolm Haak
>>>
>>> On 18/04/13 17:22, Malcolm Haak wrote:
>>>> Hi Mark!
>>>>
>>>> Thanks for the quick reply!
>>>>
>>>> I'll reply inline below.
>>>>
>>>> On 18/04/13 17:04, Mark Nelson wrote:
>>>>> On 04/17/2013 11:35 PM, Malcolm Haak wrote:
>>>>>> Hi all,
>>>>>
>>>>> Hi Malcolm!
>>>>>
>>>>>>
>>>>>> I jumped into the IRC channel yesterday and they said to email
>>>>>> ceph-devel. I have been having some read performance issues. With
>>>>>> Reads
>>>>>> being slower than writes by a factor of ~5-8.
>>>>>
>>>>> I recently saw this kind of behaviour (writes were fine, but reads
>>>>> were
>>>>> terrible) on an IPoIB based cluster and it was caused by the same TCP
>>>>> auto tune issues that Jim Schutt saw last year. It's worth a try at
>>>>> least to see if it helps.
>>>>>
>>>>> echo "0" > /proc/sys/net/ipv4/tcp_moderate_rcvbuf
>>>>>
>>>>> on all of the clients and server nodes should be enough to test it
>>>>> out.
>>>>>   Sage added an option in more recent Ceph builds that lets you work
>>>>> around it too.
>>>>>
>>>> Awesome I will test this first up tomorrow.
>>>>>>
>>>>>> First info:
>>>>>> Server
>>>>>> SLES 11 SP2
>>>>>> Ceph 0.56.4.
>>>>>> 12 OSD's  that are Hardware Raid 5 each of the twelve is made from 5
>>>>>> NL-SAS disks for a total of 60 disks (Each lun can do around 320MB/s
>>>>>> stream write and the same if not better read) Connected via 2xQDR IB
>>>>>> OSD's/MDS and such all on same box (for testing)
>>>>>> Box is a Quad AMD Opteron 6234
>>>>>> Ram is 256Gb
>>>>>> 10GB Journals
>>>>>> osd_op_theads: 8
>>>>>> osd_disk_threads:2
>>>>>> Filestore_op_threads:4
>>>>>> OSD's are all XFS
>>>>>
>>>>> Interesting setup!  QUAD socket Opteron boxes have somewhat slow and
>>>>> slightly oversubscribed hypertransport links don't they?  I wonder
>>>>> if on
>>>>> a system with so many disks and QDR-IB if that could become a
>>>>> problem...
>>>>>
>>>>> We typically like smaller nodes where we can reasonably do 1 OSD per
>>>>> drive, but we've tested on a couple of 60 drive chassis in RAID
>>>>> configs
>>>>> too.  Should be interesting to hear what kind of aggregate performance
>>>>> you can eventually get.
>>>>
>>>> We are also going to try this out with 6 luns on a dual xeon box. The
>>>> Opteron box was the biggest scariest thing we had that was doing
>>>> nothing.
>>>>
>>>>>
>>>>>>
>>>>>> All nodes are connected via QDR IB using IP_O_IB. We get 1.7GB/s on
>>>>>> TCP
>>>>>> performance tests between the nodes.
>>>>>>
>>>>>> Clients: One is FC17 the other us Ubuntu 12.10 they only have around
>>>>>> 32GB-70GB ram.
>>>>>>
>>>>>> We ran into an odd issue were the OSD's would all start in the same
>>>>>> NUMA
>>>>>> node and pretty much on the same processor core. We fixed that up
>>>>>> with
>>>>>> some cpuset magic.
>>>>>
>>>>> Strange!  Was that more due to cpuset or Ceph?  I can't imagine
>>>>> that we
>>>>> are doing anything that would cause that.
>>>>>
>>>>
>>>> More than likely it is an odd quirk in the SLES kernel.. but when I
>>>> have
>>>> time I'll do some more poking. We were seeing insane CPU usage on some
>>>> cores because all the OSD's were piled up in one place.
>>>>
>>>>>>
>>>>>> Performance testing we have done: (Note oflag=direct was yielding
>>>>>> results within 5% of cached results)
>>>>>>
>>>>>>
>>>>>> root@ty3:~# dd if=/dev/zero of=/test-rbd-fs/DELETEME bs=10M
>>>>>> count=3200
>>>>>> 3200+0 records in
>>>>>> 3200+0 records out
>>>>>> 33554432000 bytes (34 GB) copied, 47.6685 s, 704 MB/s
>>>>>> root@ty3:~#
>>>>>> root@ty3:~# rm /test-rbd-fs/DELETEME
>>>>>> root@ty3:~#
>>>>>> root@ty3:~# dd if=/dev/zero of=/test-rbd-fs/DELETEME bs=10M
>>>>>> count=4800
>>>>>> 4800+0 records in
>>>>>> 4800+0 records out
>>>>>> 50331648000 bytes (50 GB) copied, 69.5527 s, 724 MB/s
>>>>>>
>>>>>> [root@dogbreath ~]# dd of=/test-rbd-fs/DELETEME if=/dev/zero bs=10M
>>>>>> count=2400
>>>>>> 2400+0 records in
>>>>>> 2400+0 records out
>>>>>> 25165824000 bytes (25 GB) copied, 26.3593 s, 955 MB/s
>>>>>> [root@dogbreath ~]# rm -f /test-rbd-fs/DELETEME
>>>>>> [root@dogbreath ~]# dd of=/test-rbd-fs/DELETEME if=/dev/zero bs=10M
>>>>>> count=9600
>>>>>> 9600+0 records in
>>>>>> 9600+0 records out
>>>>>> 100663296000 bytes (101 GB) copied, 145.212 s, 693 MB/s
>>>>>>
>>>>>> Both clients each doing a 140GB write (2x dogbreath's RAM) at the
>>>>>> same
>>>>>> time to two different rbds in the same pool.
>>>>>>
>>>>>> root@ty3:~# rm /test-rbd-fs/DELETEME
>>>>>> root@ty3:~# dd if=/dev/zero of=/test-rbd-fs/DELETEME bs=10M
>>>>>> count=14000
>>>>>> 14000+0 records in
>>>>>> 14000+0 records out
>>>>>> 146800640000 bytes (147 GB) copied, 412.404 s, 356 MB/s
>>>>>> root@ty3:~#
>>>>>>
>>>>>> [root@dogbreath ~]# rm -f /test-rbd-fs/DELETEME
>>>>>> [root@dogbreath ~]# dd of=/test-rbd-fs/DELETEME if=/dev/zero bs=10M
>>>>>> count=14000
>>>>>> 14000+0 records in
>>>>>> 14000+0 records out
>>>>>> 146800640000 bytes (147 GB) copied, 433.351 s, 339 MB/s
>>>>>> [root@dogbreath ~]#
>>>>>>
>>>>>> Onto reads...
>>>>>> Also we found that doing iflag=direct increased read performance.
>>>>>>
>>>>>> [root@dogbreath ~]# dd of=/dev/null if=/test-rbd-fs/DELETEME bs=10M
>>>>>> count=160
>>>>>> 160+0 records in
>>>>>> 160+0 records out
>>>>>> 1677721600 bytes (1.7 GB) copied, 29.4242 s, 57.0 MB/s
>>>>>> [root@dogbreath ~]#
>>>>>> [root@dogbreath ~]# echo 1 > /proc/sys/vm/drop_caches
>>>>>> [root@dogbreath ~]# dd if=/test-rbd-fs/DELETEME of=/dev/null bs=4M
>>>>>> count=10000
>>>>>> 10000+0 records in
>>>>>> 10000+0 records out
>>>>>> 41943040000 bytes (42 GB) copied, 382.334 s, 110 MB/s
>>>>>> [root@dogbreath ~]#
>>>>>> [root@dogbreath ~]# echo 1 > /proc/sys/vm/drop_caches
>>>>>> [root@dogbreath ~]# dd if=/test-rbd-fs/DELETEME of=/dev/null bs=4M
>>>>>> count=10000 iflag=direct
>>>>>> 10000+0 records in
>>>>>> 10000+0 records out
>>>>>> 41943040000 bytes (42 GB) copied, 150.774 s, 278 MB/s
>>>>>> [root@dogbreath ~]#
>>>>>>
>>>>>>
>>>>>> So what info do you want/where do I start hunting for my wumpus?
>>>>>
>>>>> might also be worth looking at the size of the reads to see if
>>>>> there's a
>>>>> lot of fragmentation.  Also, is this kernel rbd or qemu-kvm?
>>>>>
>>>>
>>>> Thing that got us was the back-end storage was showing very low read
>>>> rates. Where as when writing we could see almost a 2xWrite rate back to
>>>> physical disk (we assume that is Journal+data as the 2x is not from the
>>>> word go but ramps up around the 3-5 second mark)
>>>>
>>>> It is kernel rbd at the moment, we will be testing qemu-kvm after
>>>> things
>>>> make sense.
>>>>
>>>>>>
>>>>>> Regards
>>>>>>
>>>>>> Malcolm Haak
>>>>>>
>>>>>>
>>>>>> --
>>>>>> To unsubscribe from this list: send the line "unsubscribe
>>>>>> ceph-devel" in
>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe
>>>> ceph-devel" in
>>>> the body of a message to majordomo@vger.kernel.org
>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>