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List:       ceph-users
Subject:    [ceph-users] Re: High ceph_osd_commit_latency_ms on Toshiba MG07ACA14TE HDDs
From:       Frank R <frankaritchie () gmail ! com>
Date:       2020-06-24 13:48:16
Message-ID: CAMuVLDO8BJVQ5b-R3zOepDtWrv3WMq5DKtDDvT67LNuXWUH=kw () mail ! gmail ! com
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fyi, there is an interesting note on disabling the write cache here:

https://yourcmc.ru/wiki/index.php?title=Ceph_performance&mobileaction=toggle_view_desktop#Drive_cache_is_slowing_you_down


On Wed, Jun 24, 2020 at 9:45 AM Benoît Knecht <bknecht@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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