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Comment by fgonzag | Hacker News Reader

The comparison isn't apples to apples though. You'd have to setup bcache or dm-cache with the NVMe drive in front of XFS to compare ZFS with L2ARC on a NVMe drive. This is stated in the article as an exotic technology, but bcache is generally considered stable.

The point still stands, ZFS is fast enough 99.99% of the time (when tuned correctly), and simplifies a lot of administrative tasks.

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> bcache is generally considered stable

Is it? How about the recent bug in Linux 4.14 that could lead to data loss with bcache (fixed in 4.14.2)? On the other hand ZFS for Linux also had a regression recently.

To be fair to bcache, that bug wasn't in the bcache code. It was in core kernel bio code and could easily have effected other subsystems.

That was someone introducing a regression in a core kernel API; bcache was just the victim.

With bcache one would have a write-back cache, so it would speed up writes as well (which would be superior to L2ARC).

Comparable to the L2ARC would be adding the NVMe as swap and then increasing the mysql buffer cache to 400GB or something (don't know if that would work without issues, though). With zswap that would even have compression.

ZFS also supports ZIL, would that improve write speeds?

Yes it would. And then it would be an apples to apples conparison. But this was not the intended result the percona team tried to show as dicussed in the comments. They sinply wanted to show that „if you throw mire hardware at it, zfs will outperform xfs with less hardware“.

Don‘t get me wrong. ZFS is an incredible masterpiece, but there are almost no realistic benchmarks. They are in favor of zfs like the benchmark from percona or in favor if other system when l2arc/zil is not used.

ZFS is “fast enough” depending on the use case.

Throwing expensive hardware at it to make it perform better than XFS is... an interesting “benchmarking” methodology.

That is mentioned in the article though:

> Of course, I could use flashcache or bcache with XFS and improve the XFS results but these technologies are way more exotic than the ZFS L2ARC.

The message you're replying to mentioned that and explicitly disagreed with it.

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