On Thu, 1 Dec 2016 18:06:38 -0600 Reed Dier wrote:

> Apologies if this has been asked dozens of times before, but most answers are 
> from pre-Jewel days, and want to double check that the methodology still 
> holds.
It does.

> Currently have 16 OSD’s across 8 machines with on-disk journals, created 
> using ceph-deploy.
> These machines have NVMe storage (Intel P3600 series) for the system volume, 
> and am thinking about carving out a partition for SSD journals for the OSD’s. 
> The drives don’t make tons of use of the local storage, so should have plenty 
> of io overhead to support the OSD journaling, as well as the P3600 should 
> have the endurance to handle the added write wear.
Slight disconnect there, money for a NVMe (which size?) and on disk
journals? ^_-
> From what I’ve read, you need a partition per OSD journal, so with the 
> probability of a third (and final) OSD being added to each node, I should 
> create 3 partitions, each ~8GB in size (is this a good value? 8TB OSD’s, is 
> the journal size based on size of data or number of objects, or something 
> else?).
Journal size is unrelated to the OSD per se, with default parameters and
HDDs for OSDs a size of 10GB would be more than adequate, the default of
5GB would do as well.

> So:
> {create partitions}
> set noout
> service ceph stop osd.$i
> ceph-osd -i osd.$i —flush-journal
> rm -f rm -f /var/lib/ceph/osd/<osd-id>/journal
Typo and there should be no need for -f. ^_^

> ln -s  /var/lib/ceph/osd/<osd-id>/journal /dev/<ssd-partition-for-journal>
Even though in your case with a single(?) NVMe there is little chance for
confusion, ALWAYS reference to devices by their UUID or similar, I prefer
the ID:
lrwxrwxrwx   1 root root    44 May 21  2015 journal -> 

> ceph-osd -i osd.$i -mkjournal
> service ceph start osd.$i
> ceph osd unset noout
> Does this logic appear to hold up?


> Appreciate the help.
> Thanks,
> Reed

Christian Balzer        Network/Systems Engineer                
ch...@gol.com           Global OnLine Japan/Rakuten Communications
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