Il 08/09/2014 17:18, Peter Lieven ha scritto: >> >> That's why we have splitting code for discard, and why we would have to >> add it for read/write too. > > Why should a guest generate such big requests.
When copying data, gparted will try using very large I/O sizes. Of course if something breaks it will just use a smaller size, but it would make performance worse. I tried now (with local storage, not virtual---but with such large block sizes it's disk bound anyway, one request can take 0.1 seconds to execute) and a 2 MB block size is 20% slower than 16 MB block size on your usual 3.5" rotational SATA disk. Paolo > Afaik the reported > limit for e.g. virtio-blk is 1024 sectors (reported through blockdev > --getmaxsect /dev/vda). > I think it was only the multiwrite_merge code causing trouble here.
