What fio test would indicate this behaviour up front? I guess something like this, but with a duration larger than this disk cache? [randwrite-4k-seq] stonewall bs=4k rw=randwrite fsync=1 > thank you for your hint - any input is appreciated. Please note that > Ceph does highly random IO (especially when having small object sizes), > AnandTech also states: > > "Some of our other tests have shown a few signs that the 870 EVO's write > performance can drop when the SLC cache runs out, but this > straightforward sequential write pass over the entire drive doesn't > reveal any such behavior. The 870 EVO's sequential write performance is > extremely consistent, even on the second write pass." [3] > > So this kind of cache handling is very interesting under the hood, > because it seems the Samsung SSD 870 Evo is able to handle sequential io > at nearly SATA line speed. However the random behaviour seems to be > inconsistent - maybe I'm able to run a big fio on the ssd once I have > one of these on my desk, but I can't promise I'll have time to. > > More interesting: We also have some Kingston SEDC450. Kingston even > promises constant write speed [4] - even when specifying lower > performance. At least those drives did not fell into my eye (but I did > not examine the situation specially). > > [4] https://www.kingston.com/en/ssd/dc450-data-center-solid-state-drive > > Best regards, > Michael > > -----Ursprüngliche Nachricht----- > Von: mailing-lists <mailing-lists@xxxxxxxxx> > Gesendet: Dienstag, 21. Februar 2023 10:21 > An: ceph-users@xxxxxxx > Betreff: Re: Do not use SSDs with (small) SLC cache > > Dear Michael, > > I don't have an explanation for your problem unfortunately, but I just > wondered that you experience a drop in performance, that this SSD > shouldn't have. Your SSDs drives (Samsung 870 EVO) should not get slower > on large writes. You can verify this on the post you've attached [1] or > here [3]. > > I am curious if replacing them with other disks will improve it. > > > [3] > https://www.anandtech.com/show/16480/the-samsung-870-evo-ssd-1tb-4tb- > review/4 > > > Best > > Ken _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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