* Richard W. M. Jones:
I tested the speed of decompression using:
$ hyperfine 'qemu-img convert -W -m 16 -f qcow2 test.qcow2.XXX -O raw
test.out'
(qemu 8.0.0-4.fc39.x86_64)
$ hyperfine 'nbdkit -U - --filter=qcow2dec file test.qcow2.XXX --run
'\''nbdcopy --request-size "$uri" test.out'\'' '
(nbdkit-1.35.11-2.fc40.x86_64)
How realistic is that? Larger cluster sizes will make random access
perform noticeably worse is some cases. Think about reading a few bytes
towards the end of the cluster. It makes a difference whether you have
to decompress 64 KiB bytes for that, or 2 MiB. As far as I understand
it, the above commands use all data decompressed, so they don't suffer
from this issue (particularly with read-ahead to deal with unfortunate
cluster boundaries).
Time to first HTTP request served after boot or something like that
might be a better comparison.
Thanks,
Florian