On Thu, Nov 22, 2012 at 1:00 PM, Dietmar Maurer <diet...@proxmox.com> wrote: >> It is a stream of compressed "grains" (data). They are out-of-order and each >> grain comes with the virtual disk lba where the data should be visible to the >> guest. >> >> The stream also contains "grain tables" and "grain directories". This >> metadata makes random read access to the file possible once you have >> downloaded the entire file (i.e. it is seekable). Although tools can choose >> to >> consume the stream in sequential order too and ignore the metadata. >> >> In other words, the format is an out-of-order stream of data chunks plus >> random access lookup tables at the end. >> >> QEMU's block/vmdk.c already has some support for this format although I >> don't think we generate out-of-order yet. >> >> The benefit of reusing this code is that existing tools can consume these >> files. > > Compression format is hardcoded to RFC 1951 (defalte). I think this is a > major disadvantage, > because it is really slow (compared to lzop).
It's a naughty thing to do but we could simply pick a new constant and support LZO as an incompatible option. The file is then no longer compatible with existing vmdk tools but at least we then have a choice of using compatible deflate or the LZO extension. VMDK already has 99% of what you need and we already have a bunch of code to handle this format. This seems like a good opportunity to flesh out VMDK support and avoid reinventing the wheel. Stefan
