On Fri, Jul 20, 2007 at 03:22:17PM +0300, Al Boldi wrote:
It wouldn't be that hard to put a backup partition table at the
beginning of an ext2/3 filesystem. No one is currently using the
space between offset 512 and 1023 bytes, and it would be an easy place
to stash a backup copy of the partition table. We wouldn't be able to
use the MBR format, since information about extended partitions are
stored scattered across the disk.
So for the sake of argument, I'll propose the following partition
backup, starting at offset 512 and going for 512 bytes to byte #1023:
offset
from 512 Description
------- -----------
0..7 Signature ASCII: "PARTBAK1"
8..9 Part-type: 1=MBR
10 # of heads
11 # sectors
12 # of partitions in the backup
13..15 Reserved (must be zero)
16..31 first part entry
...
496..511 31st partition entry
Partition entry (16 bytes)
offset description
------ -----------
0 Flags
1 Type
2..3 Reserved (must be zero)
4..11 Start LBA (little endian)
12..15 # of LBA in partition
Obviously this won't work for LVM or EFI volume partition tables, but
they have enough redundancy into their on-disk formats that it
shouldn't be an issue.
Someone want to write a stand-alone function which pulls the
information from the MBR (and extended MBR's) and put it into a 512
byte buffer? If so, I'll integrate it into mke2fs and e2fsck (so that
when the user upgrades to a new enough e2fsprogs, it will
automatically back up the partition information just before the
superblock.
- Ted
-
