On 04/21/2013 06:18 PM, Malcolm Haak wrote:
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.
This is very good to know! It makes me nervous that the slower and
not-fully-connected nature of the hypertransport interconnect on quad
socket AMD setups is causing issues. With so many threads flying around
potentially accessing remote memory and having to communicate with PCIE
slots on remote IO hubs, it could be a recipe for disaster. Your
findings may indicate this could be the case.
With proper thread pinning and local disk and network controllers on
each node, there is a chance that this could be dramatically improved.
It'd be a lot of work to test it though.
Thanks for all the pointers!
Regards
Malcolm Haak
<snip>
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...
I've seen similar things with fio on a kernel rbd block device. We
suspect that because the blocks are a non-standard size it's screwing up
the numbers being reported. The issue wasn't apparent when tests were
done against a file on a file system instead of directly against the
block device.
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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