Hi,
On 9/30/21 18:02, Igor Fedotov wrote:
Using non-default min_alloc_size is generally not recommended. Primarily
due to perfomance penalties. Some side effects (like your ones) can be
observed as well. That's simple - non-default parameters generally mean
much worse QA coverage devs and less adaptation/experience from users.
Hence they're risky.
It's Pacific release what allows to use 4K min_alloc_size
[almost/hopefully] without such penalties.
We have been using "bluestore_min_alloc_size_ssd" 4k since Luminous
12.2.2 (bluefs_alloc_size": "1048576", "bluefs_shared_alloc_size":
"65536). In luminous we first used the (then) default allocator
"stupid", and later switched to bitmap, that we are still using today
(because of issues with hybrid allocator that by now have hopefully all
been fixed).
Fortunately we haven't run into any such issues, probably because we
still use bitmap allocator.
At some point in time (Pacific?) we will redploy all OSDs with hybrid
allocator.
3) reduce main space space fragmentation by using Hybrid allocator from
scratch - OSD redeployment is required as well.
We deployed these clusters at nautilus with the default allocator,
which was bitmap I think? After redeploying condor on octopus, it
seems to be running the hybrid allocator now. So I think we've
inadvertently already carried out this action on condor.
So the preliminary take away for now seems to be that clusters running
with min_alloc size 4K is to stick with bitmap until pacific and then
re-deploy with hybrid allocator.
Gr. Stefan
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