28 февраля 2019 г. 13:03:51 GMT+03:00, Uwe Sauter <uwe.sauter.de@xxxxxxxxx> пишет:
Hi all,
thanks for your insights.
Eneko,We tried to use a Samsung 840 Pro SSD as OSD some time ago and it was a no-go; it wasn't that performance was bad, it
just didn't work for the kind of use of OSD. Any HDD was better than it (the disk was healthy and have been used in a
software raid-1 for a pair of years).
I suggest you check first that your Samsung 860 Pro disks work well for Ceph. Also, how is your host's RAM?
As already mentioned the hosts each have 64GB RAM. Each host has 3 SSDs for OSD usage. Each OSD is using about 1.3GB virtual
memory / 400MB residual memory.
Joachim,I can only recommend the use of enterprise SSDs. We've tested many consumer SSDs in the past, including your SSDs. Many
of them are not suitable for long-term use and some weard out within 6 months.
Unfortunately I couldn't afford enterprise grade SSDs. But I suspect that my workload (about 20 VMs for our infrastructure, the
most IO demanding is probably LDAP) is light enough that wearout won't be a problem.
The issue I'm seeing then is probably related to direct IO if using bluestore. But with filestore, the file system cache probably
hides the latency issues.
Igor,AFAIR Samsung 860 Pro isn't for enterprise market, you shouldn't use consumer SSDs for Ceph.
I had some experience with Samsung 960 Pro a while ago and it turned out that it handled fsync-ed writes very slowly
(comparing to the original/advertised performance). Which one can probably explain by the lack of power loss protection
for these drives. I suppose it's the same in your case.
Here are a couple links on the topic:
https://www.percona.com/blog/2018/02/08/fsync-performance-storage-devices/
https://www.sebastien-han.fr/blog/2014/10/10/ceph-how-to-test-if-your-ssd-is-suitable-as-a-journal-device/
Power loss protection wasn't a criteria for me as the cluster hosts are distributed in two buildings with separate battery backed
UPSs. As mentioned above I suspect the main difference for my case between filestore and bluestore is file system cache vs. direct
IO. Which means I will keep using filestore.
Regards,
Uwe
ceph-users mailing list
ceph-users@xxxxxxxxxxxxxx
http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
--
With best regards,
Vitaliy Filippov
_______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
