2 Dec
2020
2 Dec
'20
3 p.m.
Effective min_alloc_size stays the same after mkfs. Config modifications
don't impact it after OSD is created.
On 12/2/2020 2:51 PM, 胡 玮文 wrote:
> Thanks for your reply. But I still get some wired results.
>
> I remember that min_alloc_size cannot be changed after OSD creation, but I can’t find
the source now. Searching results in this PR[1], which state: “min_alloc_size is now fixed
at mkfs time”. Is it true that we can only change the min_alloc_size by destroying and
recreating the OSD?
>
> If it is true, then all the provided methods does not give real effective
min_alloc_size. Assuming min_alloc_size cannot be changed can’t be changed without OSD
recreation:
> * Output of “ceph daemon osd.0 config ...” shows old value (64k), but after I restart
the OSD daemon, it shows new value (32k), which can’t be correct.
> * Output of “ceph config get ...” always shows new value, which can’t be the
effective value.
>
> Or maybe my knowledge is out of date. Now we can really change the min_alloc_size by
just setting the new value and restarting the OSD daemon?
>
> [1]: https://github.com/ceph/ceph/pull/17610
>
> 在 2020年12月2日，15:56，Eugen Block <eblock(a)nde.ag> 写道：
>
> Hi,
>
> there're several ways to retrieve config information:
>
> osd-host:~ # ceph daemon osd.0 config show | grep bluestore_min_alloc_size
> "bluestore_min_alloc_size": "0",
> "bluestore_min_alloc_size_hdd": "65536",
> "bluestore_min_alloc_size_ssd": "4096",
>
> osd-host:~ # ceph daemon osd.0 config get bluestore_min_alloc_size
> {
> "bluestore_min_alloc_size": "0"
> }
>
> osd-host:~ # ceph config get osd bluestore_min_alloc_size
>
>
> osd-host:~ # ceph config get osd bluestore_min_alloc_size_hdd
> 65536
>
> osd-host:~ # ceph config get osd.0 bluestore_min_alloc_size_hdd
> 65536
>
>
> Regards,
> Eugen
>
>
> Zitat von 胡 玮文 <huww98(a)outlook.com>om>:
>
> Hi all,
>
> I’ve read from this mail list that too high bluestore_min_alloc_size will result in
too much space wasted if I have many small objects. But too low bluestore_min_alloc_size
will reduce performance. I’ve also read that this config can’t be changed after OSD
creation.
>
> Now I want to tune this config myself. I change bluestore_min_alloc_size_hdd from
default 64k to 32k, then deployed some more OSDs with cephadm. I assume old OSD will
continue to use the old setting, and new OSDs will use the new setting. But how can I
verify that? To be specific, how can I query the effective min_alloc_size for a specific
OSD?
>
> I’ve tried to use “ceph daemon osd.X ...” but cannot find the appropriate command. I
also searched the OSD logs.
>
> Thanks.
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