Il 25/11/2013 16:32, Peter Lieven ha scritto: >> >> Also, a couple of ideas for separate patches. Perhaps the default value >> of "-S" could be cluster_size if specified? This would avoid making raw >> images too fragmented, and compounding filesystem-level fragmentation >> with qcow2-level fragmentation. And 4K is too small a default in my >> opinion; it could be easily changed to 64K, though 4K was of course an >> improvement compared to 512 before commit a22f123 (qemu-img: Require >> larger zero areas for sparse handling, 2011-08-26). > I would vote for 64K or 256K, we already use the first for some time. > However, it turned out > that (much) bigger values decrease performance. Setting it > to cluster_size can be dangerous. As described in my case its 15MB and > I think for vhd its 1MB. This can be a lot of zeros that have to be > written.
What about max(4096, min(bdi->cluster_size, 1048576))? Paolo
