Hi Wido,
as bluestore_prefer_deferred_size is the parameter size of IOs to defer
writes. There was a bug report involving Igor but dont find it. There
was discussed that this value must not exceed 512KB...
Regarding osd perf it is just my assumption that when commit and apply
timing are equal that there is no deferring at all.Looking at iostat
the iosizes to spinning disks are now a lot smaller (~ 4-80KB) than
before(~>300KB).
I could imagin I hitted some bug or filled my wal and now the osds are
not deferring anymore. I remember that someone wrong a blog about
bluestore mentioning that bluestore "journaling" does only work until a
specific point. If that is reached deferring is deactivated. Could
someone bring a bit of light in this?
At the moment I get the write latency of my hdds.
Regards,Dennis
-------- Weitergeleitete Nachricht --------Von: Wido den Hollander <
wido@xxxxxxxx>An: Dennis Benndorf <dennis.benndorf@xxxxxxxxxxxxxx>,
ceph-users@ceph.ioBetreff: Re: Bluestore does not defer
writesDatum: Mon, 31 Aug 2020 16:06:37 +0200
On 31/08/2020 11:00, Dennis Benndorf wrote:
Hi,
today I recognized bad performance in our cluster. Running "watch
cephosd perf |sort -hk 2 -r" I found that all bluestore OSDs are slow
oncommit and that the commit timings are equal to their apply timings:
For exampleEvery 2.0s: ceph osd perf |sort -hk 2-
r 440
82 82430 58 58435
56 56449 53 5344
2 40 40441 30
30439 27 27 99 0
1 98 0 0 97
0 2 96 0 6
95 0 2 94 0
6 93 0 13
The once with zero commit timings are filestore and the others
arebluestore osds.I did not see this after installing the new bluestore
osds (maybe thisoccured later).Both types of osds have nvmes as
journal/db. Servers have equalcpus/ram etc.
The only tuning regarding bluestore is: bluestore_block_db_size =
69793218560 bluestore_prefer_deferred_size_hdd = 524288In order to
make a filestore like behavior, but that does not seem towork.
As far as I know is that with BlueStore apply and commit latencies are
equal.
Where did you get the idea that you could influence this with these
settings?
Wido
Any tips?
Regards Dennis_______________________________________________ceph-users
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