[ceph-users] Bluestore OSD_DATA, WAL & DB

Willem Jan Withagen wjw at digiware.nl
Fri Nov 3 07:01:35 PDT 2017

On 3-11-2017 00:09, Nigel Williams wrote:
> On 3 November 2017 at 07:45, Martin Overgaard Hansen <moh at multihouse.dk> wrote:
>> I want to bring this subject back in the light and hope someone can provide
>> insight regarding the issue, thanks.

> Is it possible to make the DB partition (on the fastest device) too
> big? in other words is there a point where for a given set of OSDs
> (number + size) the DB partition is sized too large and is wasting
> resources. I recall a comment by someone proposing to split up a
> single large (fast) SSD into 100GB partitions for each OSD.

Waisting resources is probably relative.

SSD have a limitted lifetime. And Ceph is a seriously hard (ab)user of
the wear for SSDs.

Now if you over dimension the allocated space, it looks like it is not
used. But onderneath in the SSD firmware writting is spread out over all
cells of the SSD. So the wear is evely distibuted over all componets of
the SSD.

And by overcommitting you have thus prolonged the life of you SSD.

So it is either buy more now, but less replacing.
Or allocate stricktly, and replace sooner.


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