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Re: [Qemu-devel] [PATCH v13 5/6] raw-posix: Add full preallocation optio


From: Richard W.M. Jones
Subject: Re: [Qemu-devel] [PATCH v13 5/6] raw-posix: Add full preallocation option
Date: Thu, 4 Sep 2014 14:07:14 +0100
User-agent: Mutt/1.5.20 (2009-12-10)

On Thu, Sep 04, 2014 at 02:52:57PM +0200, Kevin Wolf wrote:
> Am 04.09.2014 um 14:45 hat Richard W.M. Jones geschrieben:
> > On Thu, Sep 04, 2014 at 02:35:22PM +0200, Kevin Wolf wrote:
> > > Please change the code to always write zeros for FULL,
> > 
> > How is this useful for anyone?  You don't know if the underlying SAN
> > is going to detect these zeroes or combine these blocks together.
> > It's just slow for no reason.
> 
> It's slow for the reason that the user has requested it. Do you doubt
> that users can know what their backend is doing? Why are you insisting
> on providing only the functionality that you personally need?

I'm not!  I'm trying to make sure we don't end up with a qemu
interface which is useless for higher layers.  You're proposing
preallocation=full which will be slow but not actually give any
guarantees, or preallocation=meta which is going to be fast but may
not work, and I'm saying that's a dumb interface that's not useful.

Rich.

-- 
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