[Linux-cluster] Re: 32bits vs 64bits (was: GFS limits: fs size, etc.)

Axel Thimm Axel.Thimm at ATrpms.net
Mon Sep 13 16:55:59 UTC 2004

On Mon, Sep 13, 2004 at 11:24:32AM -0500, Ken Preslan wrote:
> On Mon, Sep 13, 2004 at 06:15:08PM +0200, Axel Thimm wrote:
> > On Fri, Sep 10, 2004 at 01:05:03PM -0500, Ken Preslan wrote:
> > > For Linux 2.6 on a 32-bit platform, the max filesystem size is 16TB if
> > > you trust the sign bit, 8TB if you don't.  This limit comes from the
> > > 32-bit page index in the "struct page": 2^32 * 4096 bytes/page = 16TB.
> > > 
> > > For Linux 2.6 on a 64-bit platform, the max filesystem size is *big*.
> > > Something around 2^64 bytes.
> > 
> > That means that you need to have a cluster of equal-bit-arch members?
> >
> > One can certainly not add a 32-bit cluster member to a 64-bit > 16TB
> > crafted cluster. What about smaller sized filesystems? Would 32bits
> > and 64bits work nicely together, or are there more barriers?
> You can happily mix 32-bit and 64-bit machines.  As you said, 32-bit
> machines shouldn't access bigger filesystems.  But, you can have a mixed
> cluster with the 32-bit machines mounting only smaller the filesystems
> and the 64-bit machines mounting anything they want.

That's good news, thank you. :)

Does this mean the on-disk-format is independent of the machine word

Just out of interest, what will happen, if a 32bit cluster member
tries to join/mount a too-large fs? Will the operation fail or will
there be silent data corruption?

(My background is that I am testing GFS/cvs under x86_64, but later
most cluster members will be ia32.)

Axel.Thimm at ATrpms.net
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