Hi Ken,
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(a)indane.de>
Gesendet: Dienstag, 21. Februar 2023 10:21
An: ceph-users(a)ceph.io
Betreff: [ceph-users] 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…
Best
Ken