Re: XFS Preallocate using ALLOCSP

[Felix Blyakher <felixb@xxxxxxx>]

On Jun 16, 2009, at 5:05 PM, Eric Sandeen wrote:

> Smit Shah wrote:
> > Since fallocate uses the RESVSP cmd for xfs. And as given given for
> > RESVSP in man page for xfsctl
> > If the  XFS filesystem  is  configured to flag unwritten file  
> > extents,
> > performance will be negatively affected when writing to preallocated
> > space, since extra filesystem transactions are required to convert
> > extent  flags  on  the  range  of  the  file  written.
> And ext4 must do basically the same thing, as would any fs that flags
> unwritten extents.
>
> ext4 may convert more at a time, though, rather than leaving
> "fragmented" written/unwritten/written/unwritten regions.
Converting more at a time would require writing extra zeros
to extra space converted, but not covered with write. Again,
it's a trade off, and there is no clear winner. Well, at least
not in my mind, until proven that some operations are more
efficient than others.

Thanks,
Felix