Yes, that is correct. No need to restart the osds. .. Dan On Thu., Jul. 14, 2022, 07:04 Zakhar Kirpichenko, <zakhar@xxxxxxxxx> wrote: > Hi! > > My apologies for butting in. Please confirm > that bluestore_prefer_deferred_size_hdd is a runtime option, which doesn't > require OSDs to be stopped or rebuilt? > > Best regards, > Zakhar > > On Tue, 12 Jul 2022 at 14:46, Dan van der Ster <dvanders@xxxxxxxxx> wrote: > >> Hi Igor, >> >> Thank you for the reply and information. >> I confirm that `ceph config set osd bluestore_prefer_deferred_size_hdd >> 65537` correctly defers writes in my clusters. >> >> Best regards, >> >> Dan >> >> >> >> On Tue, Jul 12, 2022 at 1:16 PM Igor Fedotov <igor.fedotov@xxxxxxxx> >> wrote: >> > >> > Hi Dan, >> > >> > I can confirm this is a regression introduced by >> https://github.com/ceph/ceph/pull/42725. >> > >> > Indeed strict comparison is a key point in your specific case but >> generally it looks like this piece of code needs more redesign to better >> handle fragmented allocations (and issue deferred write for every short >> enough fragment independently). >> > >> > So I'm looking for a way to improve that at the moment. Will fallback >> to trivial comparison fix if I fail to do find better solution. >> > >> > Meanwhile you can adjust bluestore_min_alloc_size_hdd indeed but I'd >> prefer not to raise it that high as 128K to avoid too many writes being >> deferred (and hence DB overburden). >> > >> > IMO setting the parameter to 64K+1 should be fine. >> > >> > >> > Thanks, >> > >> > Igor >> > >> > On 7/7/2022 12:43 AM, Dan van der Ster wrote: >> > >> > Hi Igor and others, >> > >> > (apologies for html, but i want to share a plot ;) ) >> > >> > We're upgrading clusters to v16.2.9 from v15.2.16, and our simple >> "rados bench -p test 10 write -b 4096 -t 1" latency probe showed something >> is very wrong with deferred writes in pacific. >> > Here is an example cluster, upgraded today: >> > >> > >> > >> > The OSDs are 12TB HDDs, formatted in nautilus with the default >> bluestore_min_alloc_size_hdd = 64kB, and each have a large flash block.db. >> > >> > I found that the performance issue is because 4kB writes are no longer >> deferred from those pre-pacific hdds to flash in pacific with the default >> config !!! >> > Here are example bench writes from both releases: >> https://pastebin.com/raw/m0yL1H9Z >> > >> > I worked out that the issue is fixed if I set >> bluestore_prefer_deferred_size_hdd = 128k (up from the 64k pacific default. >> Note the default was 32k in octopus). >> > >> > I think this is related to the fixes in >> https://tracker.ceph.com/issues/52089 which landed in 16.2.6 -- >> _do_alloc_write is comparing the prealloc size 0x10000 with >> bluestore_prefer_deferred_size_hdd (0x10000) and the "strictly less than" >> condition prevents deferred writes from ever happening. >> > >> > So I think this would impact anyone upgrading clusters with hdd/ssd >> mixed osds ... surely we must not be the only clusters impacted by this?! >> > >> > Should we increase the default bluestore_prefer_deferred_size_hdd up to >> 128kB or is there in fact a bug here? >> > >> > Best Regards, >> > >> > 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
 |