Hi! I have an interesting question regarding SSDs and I'll try to ask about it here. During my testing of Ceph & Vitastor & Linstor on servers equipped with Intel D3-4510 SSDs I discovered a very funny problem with these SSDs: They don't like overwrites of the same sector. That is, if you overwrite the same sector over and over again you get very low iops: $ fio -direct=1 -rw=write -bs=4k -size=4k -loops=100000 -iodepth=1 write: IOPS=3142, BW=12.3MiB/s (12.9MB/s)(97.9MiB/7977msec) And if you overwrite at least ~128k of other sectors between overwriting the same sector you get normal results: $ fio -direct=1 -rw=write -bs=4k -size=128k -loops=100000 -iodepth=1 write: IOPS=20.8k, BW=81.4MiB/s (85.3MB/s)(543MiB/6675msec) This slowdown almost doesn't hurt Ceph, slightly hurts Vitastor (the impact was greater before I added a fix), and MASSIVELY hurts Linstor/DRBD9 because of its "bitmap". By now I've only seen it on this particular model of SSD. For example, Intel P4500, Micron 9300 Pro, Samsung PM983 don't have this issue. Do you have any contacts of Intel SSD firmware guys to ask them about this bug-o-feature? :-) -- With best regards, Vitaliy Filippov _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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