I think I got over 10% improvement when I changed from cooked journal
file on btrfs based system SSD to a raw partition on the system SSD.
The cluster I've been testing with is all consumer grade stuff running
on top of AMD piledriver and kaveri based mobo's with the on-board
SATA. My SSDs are a hodgepodge of OCZ Vertex 4 and Samsung 840 and 850
(non-pro). I'm also seeing a performance win by merging individual osds
into btrfs mirror sets after doing thatand dropping the replica count
from 3 to 2. I also consider this a better defense in depth strategy
since btrfs self-heals when it hits bit rot on the mirrors and raid sets.
That boost was probably aio and dio kicking in because of the raw versus
cooked. Note that I'm running Hammer on gentoo and my current WIP is
moving kernels from 3.8 to 4.0.5 everywhere. It will be interesting to
see what happens with that.
Regards
Bill
On 09/29/2015 07:32 AM, Jiri Kanicky wrote:
Hi Lionel.
Thank you for your reply. In this case I am considering to create
separate partitions for each disk on the SSD drive. Would be good to
know what is the performance difference, because creating partitions
is kind of waste of space.
One more question, is it a good idea to move journal for 3 OSDs to a
single SSD considering if SSD fails the whole node with 3 HDDs will be
down? Thinking of it, leaving journal on each OSD might be safer,
because journal on one disk does not affect other disks (OSDs). Or do
you think that having the journal on SSD is better trade off?
Thank you
Jiri
On 29/09/2015 21:10, Lionel Bouton wrote:
Le 29/09/2015 07:29, Jiri Kanicky a écrit :
Hi,
Is it possible to create journal in directory as explained here:
http://wiki.skytech.dk/index.php/Ceph_-_howto,_rbd,_lvm,_cluster#Add.2Fmove_journal_in_running_cluster
Yes, the general idea (stop, flush, move, update ceph.conf, mkjournal,
start) is valid for moving your journal wherever you want.
That said it probably won't perform as well on a filesystem (LVM as
lower overhead than a filesystem).
1. Create BTRFS over /dev/sda6 (assuming this is SSD partition alocate
for journal) and mount it to /srv/ceph/journal
BTRFS is probably the worst idea for hosting journals. If you must use
BTRFS, you'll have to make sure that the journals are created NoCoW
before the first byte is ever written to them.
2. Add OSD: ceph-deploy osd create --fs-type btrfs
ceph1:sdb:/srv/ceph/journal/osd$id/journal
I've no experience with ceph-deploy...
Best regards,
Lionel
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