This question is related to this question: Not enough components to start the RAID array?

I'm trying to retrieve data from a "Western Digital MyBook World Edition (white light)" NAS device. This is basically an embedded Linux box with a 1TB HDD in it formatted in ext3. It stopped booting one day for no apparent reason.

I have extracted the HDD from the NAS device and installed it in a desktop machine running Ubuntu 10.10 in the hope of accessing the files on the drive. I have followed instructions in this forum post, intended to mount the drive through Terminal: http://mybookworld.wikidot.com/forum/t-90514/how-to-recover-data-from-wd-my-book-world-edition-nas-device#post-976452

I have identified the partition that I want to mount and recover files from as /dev/sd4 by running "fdisk -l" and getting this:

Disk /dev/sdb: 1000.2 GB, 1000204886016 bytes
255 heads, 63 sectors/track, 121601 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0001cf00

Device Boot Start End Blocks Id System
/dev/sdb1 5 248 1959930 fd Linux raid autodetect
/dev/sdb2 249 280 257040 fd Linux raid autodetect
/dev/sdb3 281 403 987997+ fd Linux raid autodetect
/dev/sdb4 404 121601 973522935 fd Linux raid autodetect//

When I try to mount using: "mount -t ext3 /dev/sdb4 /media/xyz" I get the following error:

mount: wrong fs type, bad option, bad superblock on /dev/sdb4,
missing codepage or helper program, or other error
In some cases useful info is found in syslog - try
dmesg | tail or so

And "dmesg | tail" shows me:

[ 15.184757] [drm] Initialized nouveau 0.0.16 20090420 for 0000:01:00.0 on minor 0
[ 15.986859] [drm] nouveau 0000:01:00.0: Allocating FIFO number 1
[ 15.988379] [drm] nouveau 0000:01:00.0: nouveau_channel_alloc: initialised FIFO 1
[ 16.353379] EXT4-fs (sda5): re-mounted. Opts: errors=remount-ro,commit=0
[ 16.705944] tg3 0000:02:00.0: eth0: Link is up at 100 Mbps, full duplex
[ 16.705951] tg3 0000:02:00.0: eth0: Flow control is off for TX and off for RX
[ 16.706102] ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
[ 19.125673] EXT4-fs (sda5): re-mounted. Opts: errors=remount-ro,commit=0
[ 27.600012] eth0: no IPv6 routers present
[ 373.478031] EXT3-fs (sdb4): error: can't find ext3 filesystem on dev sdb4.

I guess that last line is the punch line :)

Why can't it find the ext3 filesystem on my drive? What do I need to do to mount this partition and copy its contents? Does it have anything to do with the drive being part of a RAID Array (see question mentioned above)?

Many thanks to any who can help.