Good point. Thanks!
On Wed, Dec 9, 2015 at 2:41 PM, John Spray <jspray@xxxxxxxxxx> wrote:
On Wed, Dec 9, 2015 at 1:25 PM, Mykola Dvornik <mykola.dvornik@xxxxxxxxx> wrote:Hi Jan, Thanks for the reply. I see your point about replicas. However my motivation was a bit different. Consider some given amount of objects that are stored in the metadata pool. If I understood correctly ceph data placement approach, the number of objects per PG should decrease with the amount of PGs per pool. So my concern is that in catastrophic event of some PG(s) being lost I will loose more objects if the amount of PGs per pool is small. At the same time I don't want to have too few objects per PG to keep things disk IO, but not CPU bounded.If you are especially concerned about triple-failures (i.e. permanent PG loss), I would suggest you look at doing things like a size=4 pool for your metadata (maybe on SSDs). You could also look at simply segregating your size=3 metadata on to separate spinning drives, so that these comparatively less loaded OSDs will be able to undergo recovery faster in the event of a failure than an ordinary data drive that's full of terabytes of data, and have a lower probability of a triple failure. John
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