Il 18/03/2013 10:04, Kevin Wolf ha scritto: > Oh, seems I misread this then. I thought this was about internal live > snapshots, which is a feature that I consider really useful. I'm not so > sure if saving the VM state as the disk contents of a qcow2 image is > really helpful. > > If zero clusters help a lot, then there's clearly something to improve > in the migration protocol, because it shouldn't send so many zeros in > the first place.
Zero pages are sent as a single 9-byte entry (64 bits for the address and flags, 8 for the zero). I don't expect the migration stream to have a single zero cluster, since every page is prefixed by the 64 bits for the address and flags. Furthermore, the RAM data would be horribly unaligned because of this. 15-20% sectors or so would be read twice, since reading each page (4104 bytes including the address and flags) would span 10 sectors (5120 bytes). Paolo
