6 Apr
2020
6 Apr
'20
1:08 p.m.
The keyword to search for is "deferred writes", there are several
parameters that control the size and maximum number of ops that'll be
"cached". Increasing to 1 MB is probably a bad idea.
Paul
--
Paul Emmerich
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On Sat, Apr 4, 2020 at 9:41 PM <jesper(a)krogh.cc> wrote:
>
> > On Sat, Apr 4, 2020 at 4:13 PM <jesper(a)krogh.cc> wrote:
> >> Offloading the block.db on NVMe / SSD:
> >> https://docs.ceph.com/docs/mimic/rados/configuration/bluestore-config-ref/
> >>
> >> Pro: Easy to deal with - seem heavily supported.
> >> Con: As far as I can tell - this will only benefit the metadata of the
> >> osd- not actual data. Thus a data-commit to the osd til still be
> >> dominated
> >> by the writelatency of the underlying - very slow HDD.
> >
> > small writes (<= 32kb, configurable) are written to db first and
> > written back to the slow disk asynchronous to the original request.
>
> Now, that sounds really interesting - I havent been able to find that in
> the documentation - can you provide a pointer? Whats the configuratoin
> parameter named?
>
> Meaning moving block.dk to a say 256GB NVMe will do "the right thing" for
> the system and deliver a fast write cache for smallish writes.
>
> Would setting the parameter til 1MB be "insane"?
>
> Jesper
>