Large Files on IA32

Jakob Østergaard jakob at unthought.net
Sat Jul 28 17:42:26 EDT 2001


On Fri, Jul 27, 2001 at 01:10:07PM -0500, Roger L. Smith wrote:
> On Fri, 27 Jul 2001, Brian Macy wrote:
> 
> >
> > We have been trying to get support for large files (>2GB) working on
> > our PentiumIII cluster running under RedHat 6.2 with a 2.2.x
> > kernel.  In particular, most of our parallel programs are MPI
> > programs and use MPI-IO (ROMIO) to do parallel I/O.  I'm interested
> > if other people have had success with such a set up, and whether
> > they'd be interested in sharing experiences.
> 
> I have created files over 70GB in size on an xfs logical volume under
> RedHat 7.1.  This doesn't really help you much with 6.2 or the 2.2 kernel,
> I know, but I thought it was worth mentioning.  We've been using xfs on
> our head node in production for several months (under quite heavy loads),
> and haven't had any real problems with it.

Ok - just to clarify:

The 2GB limit is *not* within ext2.  If the filesystem is all you change, the
2GB limit will stay.

The limitation is in VFS, the virtual file-system layer on top of *any*
filesystem you put in Linux.

The 2.4 kernels do not have this limitation anymore.  Files larger than 2 GB
will work on 32-bit platforms on Linux 2.4 on any filesystem that supports it
(including, of course, ext2).

However, you need more than just kernel support.  Your C library must be able
to handle the bigger numbers as well.   And even with both kernel and C library
in order, your applications and the libraries they use *also* must support
this.

But don't worry - it's not so bad:  Many newer distributions, such as RH7.1,
support this out of the box.  They have 2.4 kernels and glibc to go with it.

Then all there's left is the support libraries and your own code.

-- 
................................................................
:   jakob at unthought.net   : And I see the elder races,         :
:.........................: putrid forms of man                :
:   Jakob Østergaard      : See him rise and claim the earth,  :
:        OZ9ABN           : his downfall is at hand.           :
:.........................:............{Konkhra}...............:

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