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I have a synology nas with an internal hdd (a 2TB wd ears). This drive has SMART errors. I took the drive and build it in a external USB case. Then i booted Linux mint and tried to mount the data partition:

$ mount -t ext4 /dev/sdc5
[ 5875.123929] EXT4-fs (sdc5): VFS: Can't find ext4 filesystem

comment-1 Here is the detailed data, it is not sdb, it is sdc5.

[ 3986.299096] scsi 3:0:0:0: Direct-Access     WDC WD20 EARS-00MVWB0          PQ: 0 ANSI: 2
[ 3993.436189]  sdb: sdb1 sdb2 sdb3 < sdb5 >
[ 3993.519917] sd 3:0:0:0: [sdb] Attached SCSI disk

Device Boot      Start         End      Blocks   Id  System
/dev/sdc1             256     4980735     2490240   fd  Linux raid autodetect
/dev/sdc2         4980736     9175039     2097152   fd  Linux raid autodetect
/dev/sdc3         9437184  3907015007  1948788912    f  W95 Ext'd (LBA)
/dev/sdc5         9453280  3907015007  1948780864   fd  Linux raid autodetect

I tried fsck.ext4 on the device without success:

the superblock is corrupt, and you might try running e2fsck with an alternate superblock:
e2fsck -b 8193 <device>

tried this:

e2fsck -b 8193 /dev/sdc5
--> same error.

Is it possible to rebuild the filesystem without doing damage to the data?

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Are you sure the filesystem is on /dev/sdc? That would mean the disk would be unpartitioned with the filesystem taking up the entire disk. While that's perfectly possible, it's not that usual. Does mount /dev/sdc1 perhaps work? What does cat /proc/partitions say? Are you sure the disk shows up as sdc? If it's connected with USB, you can check the output of dmesg for instance.

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+1, checking dmesg output can be really helpful. Also, you can use fdisk -l /dev/sdc. – Khaled Mar 10 '12 at 11:43
i can mount the other partitions, only sdc5 is not mountable – Max Berthold Mar 10 '12 at 11:50

You seem to be having raid partitions in the /dev/sdc device. If it is a raid partition direct mount will not work. Check the output of

cat /proc/mdstat

In there you will be able to see devices like md0, md1... mdn. You should then be able to mount your raid devices via /dev/md<x>.

share|improve this answer
It isnt a raid, the other partitions can be mounted directly. Is there a ext4 recovery tool? – Max Berthold Mar 10 '12 at 12:03
Mounting one disk/partition of a raid 1 disk should be possible. All the data is there since it's a mirror, and the metadata for mdadm is ignored. – arjarj Mar 10 '12 at 12:26

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