Well, what I was saying was "does it hurt to unconditionally run hdparm -W
0 on all disks?"
Which disk would suffer from this? I haven't seen any disk where this would
be a bad idea
Paul
--
Paul Emmerich
Looking for help with your Ceph cluster? Contact us at
croit GmbH
Freseniusstr. 31h
81247 München
Tel: +49 89 1896585 90
On Wed, Jun 24, 2020 at 5:35 PM Frank Schilder <frans(a)dtu.dk> wrote:
Yes, non-volatile write cache helps as described in
the wiki. When you
disable write cache with hdparm, it actually only disables volatile write
cache. That's why SSDs with power loss protection are recommended for ceph.
A SAS/SATA SSD without any write cache will perform poorly no matter what.
Best regards,
=================
Frank Schilder
AIT Risø Campus
Bygning 109, rum S14
________________________________________
From: Paul Emmerich <paul.emmerich(a)croit.io>
Sent: 24 June 2020 17:30:51
To: Frank R
Cc: Benoît Knecht; s.priebe(a)profihost.ag; ceph-users(a)ceph.io
Subject: [ceph-users] Re: High ceph_osd_commit_latency_ms on Toshiba
MG07ACA14TE HDDs
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
Looking for help with your Ceph cluster? Contact us at
https://croit.io
croit GmbH
Freseniusstr. 31h
81247 München
www.croit.io
Tel: +49 89 1896585 90
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
_______________________________________________
ceph-users mailing list -- ceph-users(a)ceph.io
To unsubscribe send an email to ceph-users-leave(a)ceph.io
_______________________________________________
ceph-users mailing list -- ceph-users(a)ceph.io
To unsubscribe send an email to ceph-users-leave(a)ceph.io
_______________________________________________
ceph-users mailing list -- ceph-users(a)ceph.io
To unsubscribe send an email to ceph-users-leave(a)ceph.io