strict allocate

[Jeremy Allison]

On Tue, Dec 01, 2009 at 07:01:29PM +0100, Björn Jacke wrote:
> Hi,
> On 2009-12-01 at 09:33 -0800 Jeremy Allison sent off:
> > On Tue, Dec 01, 2009 at 05:56:59PM +0100, Björn JACKE wrote:
> > > It might be a good idea to change the default of strict allocate to "yes". This
> > > makes out-of-quota situation less error prone and scenarios like in that article
> > > will improve, too.
> > > 
> > > Has anyone strong feelings against that change of defaults?
> > 
> > Yes, don't do this. It's improves performance for some
> > cases, but kills performance for others.
> 
> and it avoids samba's misbehaviour when quota limits are reached.

Which is a rare case.

> it fixes ext3 - and with ext4 we'll see no performance penalty at all when
> posix_fallocate/fallocate would be used.

Haha ! Oh ye of great faith :-).

> see above. With filesystems like ext4 or xfs we have no overhead for
> preallocation of space.

Not true. Look at the glibc implementation of posix_fallocate.

> correct me if I'm wrong but it's mostly a workaround for the extreme
> framenatations problem. it doesn't fix the we-run-out-of-quota situation and
> the fallocate for ext4 and xfs is also not yet there.

It doesn't fix the problem that strict allocate = true does,
but there's a reason strict allocate = true is not default.

You haven't convinced me of the need to change it. Numbers
and benchmarks would do that.

Jeremy.