On Wed, Mar 11, 2015 at 01:28:20PM +0300, Denis V. Lunev wrote: > Plain image expansion spends a lot of time to update image file size. > This seriously affects the performance. The following simple test > qemu_img create -f parallels -o cluster_size=64k ./1.hds 64G > qemu_io -n -c "write -P 0x11 0 1024M" ./1.hds > could be improved if the format driver will pre-allocate some space > in the image file with a reasonable chunk. > > This patch preallocates 128 Mb using bdrv_write_zeroes, which should > normally use fallocate() call inside. Fallback to older truncate() > could be used as a fallback using image open options thanks to the > previous patch. > > The benefit is around 15%.
qcow2 doesn't use bdrv_truncate() at all. It simply writes past the end of bs->file to grow the file. Can you use this approach instead?
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