The Tuesday 27 May 2014 à 17:29:16 (+0200), Paolo Bonzini wrote : > 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
That seems to be 4k aligned. It's better than I though. Best regards Benoît > > I don't know if this has any practical impact, but if the fix is easy... > > Paolo >
