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 https://croit.io croit GmbH Freseniusstr. 31h 81247 München www.croit.io Tel: +49 89 1896585 90 On Wed, Jun 24, 2020 at 5:35 PM Frank Schilder <frans@xxxxxx> 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@xxxxxxxx> > Sent: 24 June 2020 17:30:51 > To: Frank R > Cc: Benoît Knecht; s.priebe@xxxxxxxxxxxx; ceph-users@xxxxxxx > Subject: 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@xxxxxxxxx> wrote: > > > 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@xxxxxxxxxxxxx> > > 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@xxxxxxx > > > To unsubscribe send an email to ceph-users-leave@xxxxxxx > > _______________________________________________ > > ceph-users mailing list -- ceph-users@xxxxxxx > > To unsubscribe send an email to ceph-users-leave@xxxxxxx > > > _______________________________________________ > ceph-users mailing list -- ceph-users@xxxxxxx > To unsubscribe send an email to ceph-users-leave@xxxxxxx > _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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