Fragmentation on XFS

Jamie Lokier
Mon, 25 Feb 2008 16:21:27 -0000

Rob Bosch wrote:
> > Any idea why Glibc's posix_fallocate makes any difference?
> >
> > Doesn't it simply write a lot of zeros?  In that case, why
doesn't
> > rsync writing lots of data sequentially result in the same number of
> > extents?
>
> The destination server had a lot of other processes running at the same
> time.  I suspect this concurrency is causing the additional extents since
> many processes writing to the same disk array.

Oh, that's quite reasonable.
>
> I thought only 1235 extents without posix_fallocate was pretty good. Under
> cygwin and NTFS, an equivalent file was generating around 25000 extents.

I guess it will depend a lot on what the other processes are doing.

Though, did I get the right impression that NTFS generates lots of
extents for small writes even when nothing else is running?

-- Jamie