Very slow ext3 fsck

[Jeremy Sanders]

Hi -

We have an ext3 file system which is 3.5TB in size (on top of lvm). Free are
172049011 out of 854473728 4096K blocks, and 396540654 out of 427245568
inodes. This is using Scientific Linux 4.4 (a RHEL clone). The filesystem
consists of multiple backups created with rsync using --link-dest, which
hard links files which haven't been modified to the previous copy. There
are several hundred days worth of these backups.

I decided to fsck the file system, but unfortunately fsck is extremely slow.
It has been going now for 67 hours and appears to be completely cpu bound
(no obvious disk access) and stuck at the "Pass 2: Checking directory
structure" stage. It doesn't respond to a normal kill or ctrl+c.

Does anybody know whether it has got stuck in a loop, or does it really take
so long to check so many hardlinks? Would it help moving to a newer e2fsck
than RHEL provides (it has version number e2fsprogs-1.35-12.4.EL4).

Thanks

Jeremy