Hi,
I am currently working on optimizing speed for compressed QCOW2 images. We use them for templates and would also like to use them for backups, but the latter is almost infeasible because using gzip for compression is horribly slow. I tried to experiment with different options to deflate, but in the end I think its better to use a different compression algorithm for cases where speed matters. As we already have probing for it in configure and as it is widely used I would like to use LZO for that purpose. I think it would be best to have a flag to indicate that compressed blocks use LZO compression, but I would need a little explaination which of the feature fields I have to use to prevent an older (incompatible) Qemu opening LZO compressed QCOW2 images. I also have already some numbers. I converted a fresh Debian 9 Install which has an uncomressed QCOW2 size of 1158 MB with qemu-img to a compressed QCOW2. With GZIP compression the result is 356MB whereas the LZO version is 452MB. However, the current GZIP variant uses 35 seconds for this operation where LZO only needs 4 seconds. I think is is a good trade in especially when its optional so the user can choose. What are your thoughts? Peter
