On 11/02/2015 1:46 PM, 杨万元 wrote:
Hello!
We use Ceph+Openstack in our private cloud. Recently we upgrade
our centos6.5 based cluster from Ceph Emperor to Ceph Firefly.
At first,we use redhat yum repo epel to upgrade, this Ceph's
version is 0.80.5. First upgrade monitor,then osd,last client. when we
complete this upgrade, we boot a VM on the cluster,then use fio to
test the io performance. The io performance is as better as before.
Everything is ok!
Then we upgrade the cluster from 0.80.5 to 0.80.8,when we
completed , we reboot the VM to load the newest librbd. after that we
also use fio to test the io performance*.then we find the randwrite
and write is as good as before.but the randread and read is become
worse, randwrite's iops from 4000-5000 to 300-400 ,and the latency is
worse. the write's bw from 400MB/s to 115MB/s*. then I downgrade the
ceph client version from 0.80.8 to 0.80.5, then the reslut become
normal.
So I think maybe something cause about librbd. I compare the
0.80.8 release notes with 0.80.5
(http://ceph.com/docs/master/release-notes/#v0-80-8-firefly ), I just
find this change in 0.80.8 is something about read request
: librbd: cap memory utilization for read requests (Jason Dillaman)
. Who can explain this？
FWIW we are seeing the same thing when switching librbd from 0.80.7 to
0.80.8 - there is a massive performance regression in random reads. In
our case, from ~10,000 4k read iops down to less than 1,000.
We also tested librbd 0.87.1 , and found it does not have this problem -
it appears to be isolated to 0.80.8 only.
Regards
Nathan
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