On Sat, 10 Mar 2018 16:50:22 +0100
Adam Borowski <kilob...@angband.pl> wrote:

> Since we're on a btrfs mailing list, if you use qemu, you really want
> sparse format:raw instead of qcow2 or preallocated raw.  This also works
> great with TRIM.

Agreed, that's why I use RAW. QCOW2 would add a second layer of COW on top of
Btrfs, which sounds like a nightmare. Even if you would run those files as
NOCOW in Btrfs, somehow I feel FS-native COW is more efficient than emulating
it in userspace with special format files.

> > It works, just not with some of the QEMU virtualized disk device drivers.
> > You don't need to use qemu-img to manually dig holes either, it's all
> > automatic.
> It works only with scsi and virtio-scsi drivers.  Most qemu setups use
> either ide (ouch!) or virtio-blk.

It works with IDE as well.

With respect,
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