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by wtallis 2085 days ago
> This is surprisingly common behavior.

Anecdotally, consumer NVMe SSDs actually tend to not lie about it. Every time I've benchmarked a consumer NVMe SSD under Windows both with and without the "Write Cache Buffer Flushing" option, it has a profound impact on the measured performance of the SSD. I have not observed a comparable performance impact for SATA SSDs, so I suspect Microsoft's description of what that option does is inaccurate for at least one type of drive, though it is at least possible that ignoring flushes is extremely common for consumer SATA SSDs but uncommon for consumer NVMe SSDs.
1 comments
throwaway8941 2085 days ago
Sure, although the proper way to test it would be to write a lot of data to the drive, issue an fsync, and cut power in the middle of the operation. Rinse and repeat a (few) hundred times for each drive.

There's a guy on btrfs' LKML (also the author of [0]) who is diligent enough to do these tests on much of the hardware he gets, and his experience does not sound good for consumer drives.

[0]: https://github.com/Zygo/bees/

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wtallis 2085 days ago
> although the proper way to test it would be to write a lot of data to the drive, issue an fsync, and cut power in the middle of the operation. Rinse and repeat a (few) hundred times for each drive.

This isn't quite right. You have to ensure that the drive returned completion of a flush command to the OS before the plug was pulled, or else the NVMe spec does allow the drive to return old data after power is restored. Without confirming receipt of a completion queue entry for a flush command (or equivalent), this test as described is mainly checking whether the drive has a volatile write cache—and there are much easier ways to check that.

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tobias3 2085 days ago
Here is a post from him: https://lore.kernel.org/linux-btrfs/20190623204523.GC11831@h...

TLDR: Very few drives don't implement flush correctly. Notice that he mainly uses hard disks, not SSDs/NVMe. Failure often occurs when two (usually rare) things occur at once. E.g. remapping an unreadable sector while power-cycling.

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RealStickman_ 2085 days ago
Does he share the results of his tests anywhere?
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