Am 04.12.2013 17:43, schrieb Stefan Hajnoczi: > On Wed, Nov 27, 2013 at 11:07:08AM +0100, Peter Lieven wrote: >> Suggested-by: Paolo Bonzini <pbonz...@redhat.com> >> Reviewed-by: Paolo Bonzini <pbonz...@redhat.com> >> Signed-off-by: Peter Lieven <p...@kamp.de> >> --- >> qemu-img.c | 4 ++-- >> qemu-img.texi | 2 +- >> 2 files changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/qemu-img.c b/qemu-img.c >> index 9bb1f6f..8b5f3da 100644 >> --- a/qemu-img.c >> +++ b/qemu-img.c >> @@ -100,7 +100,7 @@ static void help(void) >> " '-h' with or without a command shows this help and lists the >> supported formats\n" >> " '-p' show progress of command (only certain commands)\n" >> " '-q' use Quiet mode - do not print any output (except >> errors)\n" >> - " '-S' indicates the consecutive number of bytes (defaults to >> 4k) that must\n" >> + " '-S' indicates the consecutive number of bytes (defaults to >> 64k) that must\n" >> " contain only zeros for qemu-img to create a sparse image >> during\n" >> " conversion. If the number of bytes is 0, the source will >> not be scanned for\n" >> " unallocated or zero sectors, and the destination image >> will always be\n" >> @@ -1141,7 +1141,7 @@ static int img_convert(int argc, char **argv) >> QEMUOptionParameter *out_baseimg_param; >> char *options = NULL; >> const char *snapshot_name = NULL; >> - int min_sparse = 8; /* Need at least 4k of zeros for sparse detection */ >> + int min_sparse = 128; /* Need at least 64k of zeros for sparse >> detection */ >> bool quiet = false; >> Error *local_err = NULL; > I guess a sane size would be cluster size. For a raw file 4 KB is > reasonable since that's the file system block size. in case of iscsi the cluster size could be much too high as for example my storage has a cluster_size of 15MB. > > Is it necessary to increase to 64 KB here? No, its indepent of the rest. Paolo suggested to increase it and I can confirm that for my usage case its faster than 4K.
I would drop this patch for now. Peter
