Re: [PATCH 0/1] qcow2: Skip copy-on-write when allocating a zero cluster

[Alberto Garcia]

On Tue 25 Aug 2020 09:47:24 PM CEST, Brian Foster <bfoster@redhat.com> wrote:
> My fio fallocates the entire file by default with this command. Is that
> the intent of this particular test? I added --fallocate=none to my test
> runs to incorporate the allocation cost in the I/Os.

That wasn't intentional, you're right, it should use --fallocate=none (I
don't see a big difference in my test anyway).

>> The Linux version is 4.19.132-1 from Debian.
>
> Thanks. I don't have LUKS in the mix on my box, but I was running on a
> more recent kernel (Fedora 5.7.15-100). I threw v4.19 on the box and
> saw a bit more of a delta between XFS (~14k iops) and ext4 (~24k). The
> same test shows ~17k iops for XFS and ~19k iops for ext4 on v5.7. If I
> increase the size of the LVM volume from 126G to >1TB, ext4 runs at
> roughly the same rate and XFS closes the gap to around ~19k iops as
> well. I'm not sure what might have changed since v4.19, but care to
> see if this is still an issue on a more recent kernel?

Ok, I gave 5.7.10-1 a try but I still get similar numbers.

Perhaps with a larger filesystem there would be a difference? I don't
know.

Berto