ReiserFS & Linux

The most important things I've learned while drinking with Hans Reiser and things that always saved my data on reiserfs.

• make sure you have “enough” RAM
• make sure you have working (not br0ken) RAM
• before running any –rebuild-sb or –rebuild-tree make sure you have backup!
• have the latest reiserfsprogs tools
• have a decent stable linux kernel and reiserfs support in it

ReiserFS: hdx1: found reiserfs format "3.6" with standard journal
ReiserFS: hdx1: using ordered data mode
ReiserFS: hdx1: journal params: device hda1, size 8192, journal first block 18, max trans len 1024, max batch 900, max commit age 30, max trans age 30
ReiserFS: hdx1: checking transaction log (hda1)
ReiserFS: hdx1: warning: vs-7000: search_by_entry_key: search_by_key returned item position == 0
ReiserFS: hdx1: found reiserfs format "3.6" with standard journal
ReiserFS: hdx1: using ordered data mode
ReiserFS: hdx1: journal params: device hda1, size 8192, journal first block 18, max trans len 1024, max batch 900, max commit age 30, max trans age 30
ReiserFS: hdx1: checking transaction log (hda1)
ReiserFS: hdx1: warning: vs-7000: search_by_entry_key: search_by_key returned item position == 0

 reiserfsck --rebuild-sb /dev/hdx1

Reiserfs super block in block 16 on 0x301 of format 3.6 with standard journal
Count of blocks on the device: 4883744
Number of bitmaps: 150
Blocksize: 4096
Free blocks (count of blocks - used [journal, bitmaps, data, reserved] blocks): 3430669
Root block: 4096104
Filesystem is clean
Tree height: 5
Hash function used to sort names: not set
Objectid map size 972, max 972
Journal parameters:
        Device [0x0]
        Magic [0x0]
        Size 8193 blocks (including 1 for journal header) (first block 18)
        Max transaction length 1024 blocks
        Max batch size 900 blocks
        Max commit age 30
Blocks reserved by journal: 0
Fs state field: 0x0:
sb_version: 2
inode generation number: 2442403
UUID: bfd1afad-a173-40a6-bbbe-643dc9e68a23
LABEL:
Set flags in SB:

Super block seems to be correct, but here comes the trick ..

mount -t reiserfs /dev/hda1 /media/restore
mount: wrong fs type, bad option, bad superblock on /dev/hda1,
       missing codepage or other error
       In some cases useful info is found in syslog - try
       dmesg | tail  or so

Ok .. here is a workaround to make the partition mountable again it is enough to change one byte in the super block from 0 (hash is not set) to 3 (r5 hash). It can be done by a hex editor.

hexdump -C of block #16 (reiserfs uses 4k-size blocks, numbers start with 0):

...
00000030  06 00 01 00 52 65 49 73  45 72 32 46 73 00 00 00  |....ReIsEr2Fs...|
00000040  03 00 00 00 05 00 c6 04  02 00 00 00 89 28 00 00  |......ф.....┴(..|
          ^^ 
          this byte.
...

Which can be done like ..

I used dd to copy first 512Kb from disk, then modify them and copy back to disk:

 $ dd if=/dev/hdx1 count=1000 of=/tmp/hdx1dump

then use your favourite Hexeditor to fix problem

(position 0001:0040 in this file) –> write \“03\” in position 0001:0040

and copy it back to disk

 $ dd of=/dev/hdx1 count=1000 if=/tmp/hdx1dump