[Sheepdog] [PATCH] sheep: disable object cache by default

[Liu Yuan]

On 05/09/2012 01:40 AM, MORITA Kazutaka wrote:

> I know that the object cache works well if we don't mix writeback and
> writethrough requests.  But the default cache modes of qemu and
> qemu-img are different, so, IMHO, the object cache really should
> handle the case.
> 


I still haven't yet been convinced to add this extra option. The real
culprit is qemu-img, not object cache.

> If you really don't want to disable the feature by default, how about
> just adding an option to disable the object cache?  If we can disable
> it with a sheep command line option, it's okay, at least to me.


I think adding an extra option doesn't make sense, because:

0) QEMU disable object cache as default. This is already an efficient
means to disable object cache.

1) We already wrote a document to direct users how to use qemu-img
correctly. If any casual user tries to misuse qemu-img, I don't think he
would be aware of an option to disable object cache. So if he knows of
object cache, he is supposed to handle it himself by help message and
documentation and even if any problem, he could go ask the list for the
help.

2) Since we already have 'collie vdi clone and snapshot' utility, I'd
suggest a new tool called 'collie vdi convert' to do the job of
'qemu-img convert' correctly as default and changes our README and
documentation to use collie as default. I think this could exclude those
casual users.

Thanks,
Yuan