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<h1 class="firstHeading">Advanced Find EXT2 EXT3 Backup SuperBlock</h1>
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<p>If the EXT2/EXT3 primary superblock is damaged, the filesystem can not be mounted.
</p><p>If the normal superblock is corrupted, fsck will search an alternative superblock but
may failed to find one of them. The location of the backup superblocks are
dependent on the filesystem's blocksize, this size is stored in the superblock,
so it's not known while searching for backup superblock.
To search them, running <a href="testdisk.html" title="TestDisk">TestDisk</a>,
in the Advanced menu, select the partition and choose <b>Superblock</b>.
</p><p>The superblock contains all the information about the configuration of
the filesystem. The primary copy of the superblock is stored at an
offset of 1024 bytes from the start of the partition, and it is essential
to mounting the filesystem. Since it is so important, backup copies of
the superblock are stored in block groups throughout the filesystem.
The first version of ext2 (revision 0) stores a copy at the start of
every block group, along with backups of the group descriptor block(s).
Because this can consume a considerable amount of space for large
filesystems, later revisions can optionally reduce the number of backup
copies by only putting backups in specific groups (this is the sparse
superblock feature). The groups chosen are 0, 1 and powers of 3, 5 and 7.
</p><p>Now using the value given by TestDisk, you can use fsck to repair your ext2/ext3 filesystem.
Ie if TestDisk has found a superblock at block number 24577 and a blocksize of 1024 bytes, run
</p>
<pre>
/sbin/fsck.ext3 -b 24577 -B 1024 /dev/hda1
</pre>
<p>Back to <a href="running_testdisk.html" title="Running TestDisk">Running the TestDisk Program </a>
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