Re: RBD Read performance

[Malcolm Haak <malcolm@sgi.com>]

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
>>>>>
>>>>>
>>>>> --
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