Re: Questions about the CRUSH details

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Den tors 25 jan. 2024 kl 17:47 skrev Robert Sander
> > forth), so this is why "ceph df" will tell you a pool has X free
> > space, where X is "smallest free space on the OSDs on which this pool
> > lies, times the number of OSDs". Given the pseudorandom placement of
> > objects to PGs, there is nothing to prevent you from having the worst
> > luck ever and all the objects you create end up on the OSD with least
> > free space.
> This is why you need a decent amount of PGs, to not run into statistical
> edge cases.

Yes, just take the experiment to someone with one PG only, then it can
only fill one OSD. Someone with a pool with only 2 PGs could at the
very best case only fill two and so on. If you have 100+ PGs per OSD,
the chances for many files to end up only on a few PGs becomes very

May the most significant bit of your life be positive.
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