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Date: Fri, 2 Aug 2002 15:14:21 -0700 (PDT)
From: "Randy.Dunlap" <rddunlap@osdl.org>
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To: "Albert D. Cahalan" <acahalan@cs.uml.edu>
cc: Matti Aarnio <matti.aarnio@zmailer.org>,
       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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On Fri, 2 Aug 2002, Albert D. Cahalan wrote:

| Matti Aarnio writes:
|
| >   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")
|
| You first hit the triple-indirection limit at 4 TB.
| http://www.cs.uml.edu/~acahalan/linux/ext2.gif
|
| >       - 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.
|
| The top 4 st_size bits get stolen, so it's 60-bit sizes.
| You also get the 32-bit block limit at 16 TB.
| -

For a LinuxWorld presentation in August, I have asked each of the
4 journaling filesystems (ext3, reiserfs, JFS, and XFS) what their
filesystem/filesize limits are.  Here's what they have told me.

                      ext3fs     reiserfs     JFS     XFS
max filesize:         16 TB#      1 EB       4 PB$   8 TB%
max filesystem size:   2 TB      17.6 TB*    4 PB$   2 TB!

Notes:
#: think sparse files
*: 4 KB blocks
$: 16 TB on 32-bit architectures
%: 4 KB pages
!: block device limit


-- 
~Randy

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