Has anyone ever encountered a drive with a write cache that actually
*helped*?
I haven't.
As in: would it be a good idea for the OSD to just disable the write cache
on startup? Worst case it doesn't do anything, best case it improves
latency.
Paul
--
Paul Emmerich
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On Wed, Jun 24, 2020 at 3:49 PM Frank R <frankaritchie(a)gmail.com> wrote:
fyi, there is an interesting note on disabling the
write cache here:
https://yourcmc.ru/wiki/index.php?title=Ceph_performance&mobileaction=t…
On Wed, Jun 24, 2020 at 9:45 AM Benoît Knecht <bknecht(a)protonmail.ch>
wrote:
Hi Igor,
Igor Fedotov wrote:
> for the sake of completeness one more experiment please if possible:
>
> turn off write cache for HGST drives and measure commit latency once
again.
I just did the same experiment with HGST drives, and disabling the write
cache
on those drives brought the latency down from
about 7.5ms to about 4ms.
So it seems disabling the write cache across the board would be
advisable in
our case. Is it recommended in general, or
specifically when the DB+WAL
is on
the same hard drive?
Stefan, Mark, are you disabling the write cache on your HDDs by default?
Cheers,
--
Ben
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