Here the blog I wrote about:
https://yourcmc.ru/wiki/index.php?title=Ceph_performance&mobileaction=t…
for data + SSD for journal
Filestore writes everything to the journal and only starts to flush
it to the data device when the journal fills up to the configured
percent. This is very convenient because it makes journal act as a
«temporary buffer» that absorbs random write bursts.
Bluestore can’t do the same even when you put its WAL+DB on SSD.
It also has sort of a «journal» which is called «deferred write
queue»,
but it’s very small (only 64 requests) and it lacks any kind of
background flush threads. So you actually can increase the maximum
number of deferred requests, but after the queue fills up the
performance will drop until OSD restarts.
Maybe I have been hitten by that. Is there any change planned or done
on this?
Cant imagine users regulary restart their osds to get performance
back....
Regards,
Dennis
-------- Weitergeleitete Nachricht --------Von: Wido den Hollander <
wido(a)42on.com>An;An: Dennis Benndorf <dennis.benndorf(a)googlemail.com>om>,
ceph-users(a)ceph.ioBetreff: Re: [ceph-users] 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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