Ancestors

Written by Tomas Vondra on 2025-01-20 at 12:01

A couple weeks ago I upgraded one my home lab machines I use for benchmarking. Aside from getting a new Ryzen, the main change was getting a bunch of Samsung 990 PRO M.2 SSDs for storage. And the performance I'm seeing is rather atrocious :-(

For most workloads (reads/writes, sequential/random) it works fine, e.g. for random writes I can get ~50k IOPS (iodepth=1) quite easily. But as soon as I ask fio to do fsyncs (fsync=1), the performance just absolutely tanks to ~200 IOPS.

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Written by Tomas Vondra on 2025-01-20 at 12:01

Of course, fsync=1 is expected to have some impact. Every SSD I own shows the same effect, but never this bad. For example:

WD Ultrastar SN640: 50k => 40k IOPS

Intel DC S3700 (6x RAIO0): 24k => 6k IOPS

So the drop 50k => 200 IOPS seems terrible. What am I doing wrong? Any suggestions for a better option (device/model) - still affordable, but handling fsync reasonably?

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Toot

Written by AndresFreundTec on 2025-01-20 at 14:53

@tomasv FWIW, I would actually have trouble believing that the SN640 is doing correct fsyncs. That's not a big enough drop IME. It's also far less than what I have observed with newer WD NVMes.

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Descendants

Written by Tomas Vondra on 2025-01-20 at 15:01

@AndresFreundTec Not sure, but it's an Ultrastar drive targeted at DC workloads, not a regular consumer drive. Of course, "enterprise" is just a label ...

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Written by AndresFreundTec on 2025-01-20 at 16:15

@tomasv Possible. My experience is that either there's basically no drop (because there's a supercap or such that allows writes to be flushed before loosing power, making cache flushes free), or there's a more significant drop than 20%.

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