On Tue, Apr 13, 2021 at 12:35 PM Mark Nelson <mnelson@xxxxxxxxxx> wrote: > > On 4/13/21 4:07 AM, Dan van der Ster wrote: > > > On Tue, Apr 13, 2021 at 9:00 AM Wido den Hollander <wido@xxxxxxxx> wrote: > >> > >> > >> On 4/12/21 5:46 PM, Dan van der Ster wrote: > >>> Hi all, > >>> > >>> bdev_enable_discard has been in ceph for several major releases now > >>> but it is still off by default. > >>> Did anyone try it recently -- is it safe to use? And do you have perf > >>> numbers before and after enabling? > >>> > >> I have done so on SATA SSDs in a few cases and: it worked > >> > >> Did I notice a real difference? Not really. > >> > > Thanks, I've enabled it on a test box and am draining data to check > > that it doesn't crash anything. > > > >> It's highly debated if this still makes a difference with modern flash > >> devices. I don't think there is a real conclusion if you still need to > >> trim/discard blocks. > > Do you happen to have any more info on these debates? As you know we > > have seen major performance issues on hypervisors that are not running > > a periodic fstrim; we use similar or identical SATA ssds for HV local > > storage and our block.db's. If it doesn't hurt anything, why wouldn't > > we enable it by default? > > > There's some good discussion in the original PR: > > > https://github.com/ceph/ceph/pull/14727 > > > I suspect that the primary concerns for enabling it by default are two > fold: (1) the issue of having to maintain a blocklist for buggy firmware > implementations (2) Even "good" firmware can potentially see slowdowns > with bursts of trim commands due to needing to update the FTL metadata > per this comment: > > > https://github.com/ceph/ceph/pull/14727#issuecomment-342399578 > > > The original issue of how to decide between online discard, periodic > bulk discard, or no discard is still an issue imho. I think we probably > need to get more feedback from people with real large deployments (hint > hint :D) before we enable online discard by default. Thanks for the links. And further to those I found the attempt at a periodic discard: https://github.com/ceph/ceph/pull/20723 Igor posted some performance numbers there for online and periodic, both of which seem not very promising. And I didn't find any further work on periodic discard for bitmap or beyond. Since the runtime performance impact of this looks unpredictable, maybe a conservative way to resume this work would be to allow discard via the offline bluestore tooling? Cheers, Dan > > > Mark > > > > > > Cheers, Dan > > _______________________________________________ > > 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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