On Tuesday, October 20, 2020 4:01 PM, Kevin Wolf wrote: > Am 20.10.2020 um 03:31 hat Wang, Wei W geschrieben: > > Hi, > > > > Does anyone know the reason why raw-format.c doesn't have > compression > > support (but qcow has the supported added)? For example, raw image > > backup with compression, "qemu-img convert -c -O raw origin.img > > dist.img", doesn't work. > > A raw image is by definition a file that contains the exact same sequence of > bytes as the guest sees, without any additional information or encoding. If > you compress a raw file, the guest will see compressed data on its hard disk > instead of the real data.
Ok, thanks. I'm thinking QEMU could do decompression of the compressed data in raw.img when guest reads data. > > Anything you could do to add transparent compression to it would mean that > it's not a raw image any more, but a new image format. > Yes, decompression makes it transparent to the guest. Would you think it's good to reuse the raw image implementation, just add the compress/decompress option? Thanks, Wei