Il 27/05/2014 18:00, Benoît Canet ha scritto:
> Are you worried that the host file system will lay out data poorly
> because the file looks like this?
>
> | header (1C) | refcounts (2C) | L1 (512B) | hole | Next cluster |
>
> B = bytes
> C = clusters
>
> My guess is the next cluster will be aligned to a reasonable boundary on
> the physical disk.
I have some kind of doubt. Does anyone knows a filesystem guru ?
Not a guru, but indeed there is a risk that the layout will be worse
than necessary.
I think holes are ignored unless they are big enough, but 64K-512 is
probably enough to create one. Indeed here I get this:
$ qemu-img create -f qcow2 foo.qcow2 10G
$ qemu-io -c 'write 0 512' foo.qcow2
$ qemu-img map -f raw foo.qcow2 10G
Offset Length Mapped to File
0 0x31000 0 foo.qcow2
0x40000 0x20000 0x40000 foo.qcow2
I don't know if this has any practical impact, but if the fix is easy...
Paolo
