Hi Jonas,
From your readme:
"the best possible solution is some OSDs having an offset of 1 PG to the ideal count. As a PG-distribution-optimization is done per pool, without checking other pool's distribution at all, some devices will be the +1 more often than others. At worst one OSD is the +1 for each pool in the cluster."
That's an interesting observation/flaw which hadn't occurred to me before. I think we don't ever see it in practice in our clusters because we do not have multiple large pools on the same osds.
How large are the variances in your real clusters? I hope the example in your readme isn't from real life??
Cheers, Dan
On Wed, 20 Oct 2021, 15:11 Jonas Jelten, <jelten@xxxxxxxxx> wrote:
Hi!
I've been working on this for quite some time now and I think it's ready for some broader testing and feedback.
https://github.com/TheJJ/ceph-balancer
It's an alternative standalone balancer implementation, optimizing for equal OSD storage utilization and PG placement across all pools.
It doesn't change your cluster in any way, it just prints the commands you can run to apply the PG movements.
Please play around with it :)
Quickstart example: generate 10 PG movements on hdd to stdout
./placementoptimizer.py -v balance --max-pg-moves 10 --only-crushclass hdd | tee /tmp/balance-upmaps
When there's remapped pgs (e.g. by applying the above upmaps), you can inspect progress with:
./placementoptimizer.py showremapped
./placementoptimizer.py showremapped --by-osd
And you can get a nice Pool and OSD usage overview:
./placementoptimizer.py show --osds --per-pool-count --sort-utilization
Of course there's many more features and optimizations to be added,
but it served us very well in reclaiming terrabytes of until then unavailable storage already where the `mgr balancer` could no longer optimize.
What do you think?
Cheers
-- Jonas
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