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Date: Wed, 31 Jul 2002 23:04:12 +0300
From: Matti Aarnio <matti.aarnio@zmailer.org>
To: Christoph Hellwig <hch@infradead.org>,
       "Peter J. Braam" <braam@clusterfs.com>, linux-kernel@vger.kernel.org
Subject: Re: BIG files & file systems
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References: <20020731131620.M15238@lustre.cfs> <20020731202638.A22765@infradead.org>
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In-Reply-To: <20020731202638.A22765@infradead.org>; from hch@infradead.org on Wed, Jul 31, 2002 at 08:26:38PM +0100
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On Wed, Jul 31, 2002 at 08:26:38PM +0100, Christoph Hellwig wrote:
> On Wed, Jul 31, 2002 at 01:16:20PM -0600, Peter J. Braam wrote:
> > Hi, 
> > 
> > I've just been told that some "limitations" of the following kind will
> > remain:
> > 
> >   page index = unsigned long
> >   ino_t      = unsigned long
> > 
> > Lustre has definitely been asked to support much larger files than
> > 16TB.  Also file systems with a trillion files have been requested by
> > one of our supporters (you don't want to know who, besides I've no
> > idea how many bits go in a trillion, but it's more than 32).
> 
> What about using 64bit machines? ..

  It depends on many things:
   - Block layer (unsigned long)
   - Page indexes (unsigned long)
   - Filesystem format dependent limits
      - EXT2/EXT3: u32_t FILESYSTEM block index, presuming the EXT2/EXT3
                   is supported only up to 4 kB block sizes, that gives
                   you a very hard limit.. of 16 terabytes (16 * "10^12")
      - ReiserFS:  u32_t block indexes presently, u64_t in future;
                   block size ranges ?   Max size is limited by the
                   maximum supported file size, likely 2^63, which is
                   roughly  8 * "10^18", or circa 500 000 times larger
                   than EXT2/EXT3 format maximum.
      - ClusterFS: (Braam et.al.): 64 bit block indexes ?
                   System file size limitation, same as with ReiserFS.

      (Just to illustriate a few..)


/Matti Aarnio
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