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SubjectRe: Storage Limitations
   Date: 	Thu, 1 Oct 1998 20:39:41 +0200 (CEST)
From: Rik van Riel <>

You might want to try ext2 filesystems with SPARSE superblocks
(-s 1 option). Please note that you do have to use recent kernels
in order to properly support it. Up to 2.1.122 it basically
worked, but there was a bug with the statistics... 2.1.123 has
the statistics fixed, but might have other problems.

Actually, sparse superblocks have been supported in the kernel for a
long time (since roughly Summer, 1997). They haven't been used much
because the 2.0 kernel doesn't support them, so I haven't advertised
them much. It's still the case that if you need 2.0 kernels to be able
to mount your filesystem, you may not want to use the sparse superblock
option yet.

The only bug in kernels up until recently was that df would give you
incorrect statistics about the number of free blocks, since the statfs
wasn't taking into the account the sparse superblock option. But I very
much doubt there are any other problems with that option.

The only change that was needed in the kernel (besides the statfs fix)
was in balloc.c, so that it didn't complain at mount time when it found
blocks which it thought should have been in use by the spare copies of
the superblocks, but which were free due to the sparse superblock
option. Most of the changes needed to support it were in mke2fs and
e2fsck (and in the libext2fs library).

- Ted

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