On 03/25/2013 04:07 PM, Peter_Jung@xxxxxxxx wrote:
Hi,
I have a couple of HW provisioning questions in regards to SSD for OSD
Journals.
I’d like to provision 12 OSDs per a node and there are enough CPU
clocks and Memory.
Each OSD is allocated one 3TB HDD for OSD data – these 12 * 3TB HDDs
are in non-RAID.
For increasing access and (sequential) write performance, I’d like to
put 2 SSDs for OSD journals – these two SSDs are not mirrored.
By the rule of thumb, I’d like to mount the OSD journals (the path
below) to the “SSD partitions” accordingly.
_/var/lib/ceph/osd/$cluster-$id/journal_
Question 1.
Which way is recommended between:
(1) Partitions for OS/Boot and 6 OSD journals on #1 SSD, and
partitions for the rest 6 OSD journals on #2 SSD;
(2) OS/Boot partition on #1 SSD, and separately 12 OSD journals on #2 SSD?
BTW, for better utilization of expensive SSDs, I prefer the first way.
Should it be okay?
Question 2.
I have several capacity options for SSDs.
What’s the capacity requirement if there are 6 partitions for 6 OSD
journals on a SSD?
If it’s hard to generalize, please provide me with some guidelines.
Journal size is configurable in the /etc/ceph/ceph.conf so if you have a
journal size of 10 000, you'll need 10G for 1 journal so for 6 it should
be 60G add a safety factor (ie. 20%) and you should be ok.
The size itself is 2 * desired throughput * interval between sync, so if
you have a hard drive that is able to do 100MB/s and want to have an
interval of 50s (not sure it's highly recommended) then you'll need 2 *
100 * 50 = 10 000 as the journal size.
Matthieu.
Thanks,
Peter
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