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@42on.com> 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. Mark
Cheers, Dan _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-leave@ceph.io