Comment by SamReidHughes
4 years ago
On my benchmarking of some consumer HDD's, back in 2013 or so, the flush time was always what you'd expect based on the drive's RPM. I got no evidence the drive was lying to me. These were all 2.5" drives.
My understanding was, the capacitor thing on HDD's is to ensure it completely writes out a whole sector, so it passes the checksum. I only heard the flush cache thing with respect to enterprise SSD's. But I haven't been staying on top of things.
You can't base spinning rust flushes on RPM; the seek arm is what dominates.
Not at all, and it certainly wasn't relevant to the benchmarking I was doing, as I was focusing on writes to and fsync performance for the same track.
You definitely weren't testing the cache in a meaningful way if you were hovering over the same track.
WRT to the capacitor thing being about a single sector, think about the time spans. You should be able to even cut out the drive motor power, and still stay up for 100s of ms. In that time you can seek to a config track and blit out the whole cache. If you're already writing a sector you'll be done in microseconds. The whole track spins around every ~8ms at 7200RPM.
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