Re: [Qemu-devel] [PATCH] qemu-img: Add cache command line option

[Christoph Hellwig]

On Wed, Jun 15, 2011 at 09:46:10AM -0400, Federico Simoncelli wrote:
> qemu-img currently writes disk images using writeback and filling
> up the cache buffers which are then flushed by the kernel preventing
> other processes from accessing the storage.
> This is particularly bad in cluster environments where time-based
> algorithms might be in place and accessing the storage within
> certain timeouts is critical.
> This patch adds the option to choose a cache method when writing
> disk images.

Allowing to chose the mode is of course fine, but what about also
choosing a good default?  writethrough doesn't really make any sense
for qemu-img, given that we can trivially flush the cache at the end
of the operations.  I'd also say that using the buffer cache doesn't
make sense either, as there is little point in caching these operations.