Re: XFS mounted with 'discard' option - deleting fio test files slow

[Christoph Hellwig]

On Fri, Sep 08, 2017 at 09:34:02AM +1000, Dave Chinner wrote:
> 4k random write with direct IO. 5GB file. Probably got a million 4k
> extents in it. Which means XFS has sent a million tiny 4k discards
> to the device. Run 'xfs_bmap -vvp fio_test_file.*' to confirm.
> 
> Don't use "-o discard" if you care about performance.

And your device sucks :)

Some numbers here:

https://events.linuxfoundation.org/sites/events/files/slides/discard_0.pdf

Discard will cause extra work, and for worst case sceanarios lots of
it.  But some device handle that extra load very well.