Hi,
I have a few questions about performance before putting ceph in
production. I have a test lab with 3 hosts and 2 OSD each (on dedicated
disks)
The disks have about 100MB/sec write throughput.
I noticed that when the journal is on the OSD itself, the write
throughput is only around 35MB/sec because there are two simultaneous
writes on the disk. With journal on SSD I have 100MB/sec and more write
speed.
I use block devices so, I don't have any mds.
My questions :
* Is there a way to have a good disk bandwidth without using SSD for
journal ?
* What are your recommendations ?
* Should mds help in improving this write throughput ? (Remember, I am
using block devices)
Here are my test lab results :
fred@ceph1:~$ ceph osd tree
# id weight type name up/down reweight
-1 6 root default
-3 6 rack unknownrack
-2 2 host ceph1
0 1 osd.0 up 1
1 1 osd.1 up 1
-4 2 host ceph2
2 1 osd.2 up 1
3 1 osd.3 up 1
-5 2 host ceph3
4 1 osd.4 up 1
5 1 osd.5 up 1
* host ceph1 is setup with a disk for system and two dedicated HDD for
OSD
* host ceph3 is setup with a disk for system, SSD for journals and two
dedicated HDD for OSD
Let's bench :
2013-04-22 11:41:21.843396 osd.4 [INF] bench: wrote 1024 MB in blocks of
4096 KB in 2.629238 sec at 389 MB/sec
2013-04-22 11:41:26.536869 osd.5 [INF] bench: wrote 1024 MB in blocks of
4096 KB in 4.194540 sec at 244 MB/sec
2013-04-22 11:41:43.758835 osd.0 [INF] bench: wrote 1024 MB in blocks of
4096 KB in 29.455098 sec at 35599 KB/sec
2013-04-22 11:41:46.278314 osd.1 [INF] bench: wrote 1024 MB in blocks of
4096 KB in 29.944204 sec at 35017 KB/sec
We can see that the host with HDD journal is working really slow, and
the host with SSD journal really fast --> Faster than the HDD themselves !
Besides, do the SSD journal work as SSD cache ?
Best Regards,
Fred
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