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Hi,
Success at last!
According to the ext2 documentation, the superblocks (redundant copies) are
stored at the beginning of each block group. Now the e2fsk manpage assumes
that the group size is 8192 blocks. So it says that the superblocks will be
located at (n x 8192)+1. But that is not the real case!
All you need to do is a dumpe2fs. This will give you the actual number of
blocks in each group. The primary superblock is located at "0" (now that
seems obvious in retrospect). In my case, dumpe2fs reports that the group
size is 32768. So all my alternate superblocks are located at (n x
32768)+1. I checked, and they were really there!
So that solves one problem. Now I wonder if it is safe to assume that I can
restore a filesystem that is lost due to a power outage using one of these
alternate superblocks.
e2fsck -b <superblock> <device>
There is an informative introduction on the ext filesystem variants at
http://khg.redhat.com/HyperNews/get/fs/fs.html
http://e2fsprogs.sourceforge.net/ext2.html
Sameer.
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