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Message-ID: <ZEzxYc0CaPLZ9vhK@ioniq>
Date: Sat, 29 Apr 2023 12:28:49 +0200
From: Marcos Dione <mdione@...lic.org.ar>
To: linux-ext4@...r.kernel.org
Subject: Recover partition
Hi all, brand new here. I'm trying to salvage an ext4 fs on an SSD that
suddenly has 1800 bad sectors. Let's start from the partition table:
Device Boot Start End Sectors Size Id Type
/dev/sdc1 * 2048 249855 247808 121M 83 Linux
/dev/sdc2 251902 488396799 488144898 232.8G 5 Extended
/dev/sdc5 251904 488396799 488144896 232.8G 83 Linux
I don't know on what drugs I was on when I partitioned thid disk, but we have
/boot on /dev/sdc1 and / on /dev/sdc5. Trying to mount / gives errors about the
superblock. Also notice the gap between sdc1 and sdc2, there are
2047 sectors/1048064 bytes unused in the middle. this is not big enough for f.i.
a swap partition. For reference, here are the offsets in hex:
sector offset hex
2048 1_048_576 0x00_10_00_00
251904 128_974_848 0x07_b0_00_00
Weirdly, most of the bad sectors are after position 738_197_504/0x2c_00_00_00,
way past where sdc5's SB should be, and none at the exact places where the copies
are. Because of the bas sectors, the first thing I did was to make a copy of the
whole disk.
This is not the first time I play with these things[1], so I know I
should be looking for '0x53ef' in a position ending in 0x38:
# hexdump -C sdc.img | grep -E '30 .* 53 ef'
00100430 6b b3 2d 64 00 00 ff ff 53 ef 01 00 01 00 00 00 |k.-d....S.......|
00900430 09 94 57 5c 00 00 ff ff 53 ef 00 00 01 00 00 00 |..W\....S.......|
01900430 09 94 57 5c 00 00 ff ff 53 ef 00 00 01 00 00 00 |..W\....S.......|
02900430 09 94 57 5c 00 00 ff ff 53 ef 00 00 01 00 00 00 |..W\....S.......|
03101830 f0 3e 65 5c 02 00 ff ff 53 ef 01 00 01 00 00 00 |.>e\....S.......|
03106830 f0 3e 65 5c 02 00 ff ff 53 ef 01 00 01 00 00 00 |.>e\....S.......|
0310b030 f0 3e 65 5c 02 00 ff ff 53 ef 01 00 01 00 00 00 |.>e\....S.......|
0310e430 f0 3e 65 5c 02 00 ff ff 53 ef 01 00 01 00 00 00 |.>e\....S.......|
03119030 f0 3e 65 5c 02 00 ff ff 53 ef 01 00 01 00 00 00 |.>e\....S.......|
033b6830 f0 3e 65 5c 02 00 ff ff 53 ef 01 00 01 00 00 00 |.>e\....S.......|
033bcc30 f0 3e 65 5c 02 00 ff ff 53 ef 01 00 01 00 00 00 |.>e\....S.......|
033d3430 f0 3e 65 5c 02 00 ff ff 53 ef 01 00 01 00 00 00 |.>e\....S.......|
035a1630 b1 d4 f9 5c 74 f8 72 30 53 ef 26 c5 ed b7 98 fb |...\t.r0S.&.....|
03900430 09 94 57 5c 00 00 ff ff 53 ef 00 00 01 00 00 00 |..W\....S.......|
04900430 09 94 57 5c 00 00 ff ff 53 ef 00 00 01 00 00 00 |..W\....S.......|
067f4d30 84 6a 4f 21 e4 d3 39 af 53 ef 7d 95 1e 36 ff a2 |.jO!..9.S.}..6..|
0fb02e30 17 94 57 5c 00 00 ff ff 53 ef 00 00 01 00 00 00 |..W\....S.......|
1fb02e30 17 94 57 5c 00 00 ff ff 53 ef 00 00 01 00 00 00 |..W\....S.......|
2fb00030 17 94 57 5c 00 00 ff ff 53 ef 00 00 01 00 00 00 |..W\....S.......|
3fb00030 17 94 57 5c 00 00 ff ff 53 ef 00 00 01 00 00 00 |..W\....S.......|
4fb00030 17 94 57 5c 00 00 ff ff 53 ef 00 00 01 00 00 00 |..W\....S.......|
^C
The output is quite troubling. It's like we have four different sets of
superblock copies, and then some hits that are probably just random data. I say
troubling because I would have expected two sets, not four. In any case, the
ones starting at 0x0f_b0_2e_30 look quite promising. Let's see if they are in the
expected places:
# mkfs.ext4 -n /dev/sdc5
mke2fs 1.44.5 (15-Dec-2018)
Creating filesystem with 61018112 4k blocks and 15261696 inodes
Filesystem UUID: 32faf3a4-1892-4ebc-802e-fc740234bca5
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
4096000, 7962624, 11239424, 20480000, 23887872
Let's check those offsets:
In [2]: copies = [ 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
...: 4096000, 7962624, 11239424, 20480000, 23887872 ]
In [7]: for copy in copies:
...: offset = copy * 4 * 1024 # 4k blocks
...: disk_offset = offset + 128_974_848
...: print(f'{copy:8} {offset:16} {disk_offset:16} {disk_offset:14x}')
...:
# block partition offset disk offset hex
32768 134217728 263192576 fb00000
98304 402653184 531628032 1fb00000
163840 671088640 800063488 2fb00000
229376 939524096 1068498944 3fb00000
294912 1207959552 1336934400 4fb00000
819200 3355443200 3484418048 cfb00000
884736 3623878656 3752853504 dfb00000
1605632 6576668672 6705643520 18fb00000
2654208 10871635968 11000610816 28fb00000
4096000 16777216000 16906190848 3efb00000
7962624 32614907904 32743882752 79fb00000
11239424 46036680704 46165655552 abfb00000
20480000 83886080000 84015054848 138fb00000
23887872 97844723712 97973698560 16cfb00000
The numbers look promising:
* The first two entries seem to be 0x2e00 bytes off, so I'm not going to try that.
* The next three are exact matches!
But:
mdione@...blo:~/recover$ sudo fsck.ext4 -b 163840 -n /dev/sdc5
e2fsck 1.47.0 (5-Feb-2023)
Journal superblock has an unknown read-only feature flag set.
Abort? no
Journal superblock is corrupt.
Fix? no
fsck.ext4: The journal superblock is corrupt while checking journal for /dev/sdc5
e2fsck: Cannot proceed with file system check
/dev/sdc5: ********** WARNING: Filesystem still has errors **********
And:
mdione@...blo:~/recover$ for copy in 163840 229376 294912 819200 884736 1605632 \
2654208 4096000 7962624 11239424 20480000 23887872; do \
if sudo fsck.ext4 -b $copy -n /dev/sdc5 &> /dev/null; then
echo $copy;
break;
fi;
done;
echo failed
failed
So we get to the questions section:
a) Does my disk math check? It took me those 2-3 weeks to figure out how to map
the block numbers to disk offsets.
b) Besides the two random hits, why would I have what look like _four_ sets of
superblock copies?
c) Why would copies #1 and #2 seem to be in the wrong offest? Could it be that
the mkfs version I'm using now calculates different offsets from the one
I used 3-4 years ago to create those filesystems?
d) The big question: Why could it be finding the SB copies corrupted?
e) Most important one: What else can I do?
Thanks in advance any light you might shed on this. Cheers,
-- Marcos.
--
[1] https://www.grulic.org.ar/~mdione/glob/posts/recovering-partitions-with-pen-and-paper/
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