Re: [Qemu-devel] [PATCHv3 1.8 8/9] qemu-img: increase min_sparse to 128 sectors (64kb)

[Stefan Hajnoczi]

On Wed, Nov 27, 2013 at 11:07:08AM +0100, Peter Lieven wrote:
> Suggested-by: Paolo Bonzini <address@hidden>
> Reviewed-by: Paolo Bonzini <address@hidden>
> Signed-off-by: Peter Lieven <address@hidden>
> ---
>  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.

Is it necessary to increase to 64 KB here?