Just ran into an uncomfortable problem. I usually never save any documents on my machine, and keep all my stuff on an external USB hard disk. (an 80GB TrekStor DS microdisk q.u)
Well yesterday this disk just would not mount.
Read through related posts but nothing seemed to work. Even tried it on a Windows machine.

Tried TestDisk utility. Found nothing wrong with the drive, but still could not repair the MBR.

Here is the log.

-----------------------------
Fri Sep 11 16:34:17 2009
Command line: TestDisk

TestDisk 6.11.3, Data Recovery Utility, May 2009
Christophe GRENIER <grenier@cgsecurity.org>
http://www.cgsecurity.org
OS: Linux, kernel 2.6.30.5-43.fc11.x86_64 (#1 SMP Thu Aug 27 21:39:52 EDT 2009)
Compiler: GCC 3.4 - May 6 2009 14:37:46
ext2fs lib: 1.35, ntfs lib: 10:0:0, reiserfs lib: 0.3.1-rc8, ewf lib: 20080501
/dev/sda: LBA, HPA, LBA48, DCO support
/dev/sda: size 625142448 sectors
/dev/sda: user_max 625142448 sectors
/dev/sda: native_max 625142448 sectors
/dev/sda: dco 625142448 sectors
Warning: can't get size for Disk /dev/mapper/control - 0 B - CHS 1 1 1, sector size=512
/dev/mapper/vg_linuxem64t-lv_root: LBA, HPA, LBA48, DCO support
/dev/mapper/vg_linuxem64t-lv_root: size 612564992 sectors
/dev/mapper/vg_linuxem64t-lv_root: user_max 625142448 sectors
/dev/mapper/vg_linuxem64t-lv_root: native_max 625142448 sectors
/dev/mapper/vg_linuxem64t-lv_root: dco 625142448 sectors
/dev/mapper/vg_linuxem64t-lv_swap: LBA, HPA, LBA48, DCO support
/dev/mapper/vg_linuxem64t-lv_swap: size 12156928 sectors
/dev/mapper/vg_linuxem64t-lv_swap: user_max 625142448 sectors
/dev/mapper/vg_linuxem64t-lv_swap: native_max 625142448 sectors
/dev/mapper/vg_linuxem64t-lv_swap: dco 625142448 sectors
/dev/dm-0: LBA, HPA, LBA48, DCO support
/dev/dm-0: size 612564992 sectors
/dev/dm-0: user_max 625142448 sectors
/dev/dm-0: native_max 625142448 sectors
/dev/dm-0: dco 625142448 sectors
/dev/dm-1: LBA, HPA, LBA48, DCO support
/dev/dm-1: size 12156928 sectors
/dev/dm-1: user_max 625142448 sectors
/dev/dm-1: native_max 625142448 sectors
/dev/dm-1: dco 625142448 sectors
Hard disk list
Disk /dev/sda - 320 GB / 298 GiB - CHS 38913 255 63, sector size=512 - ATA WDC WD3200BEVS-0
Disk /dev/sdb - 1000 GB / 931 GiB - CHS 121601 255 63, sector size=512 - Seagate FreeAgent
Disk /dev/sdc - 80 GB / 74 GiB - CHS 9729 255 63, sector size=512 - TrekStor DS microdisk q.u
Disk /dev/mapper/vg_linuxem64t-lv_root - 313 GB / 292 GiB - CHS 612564992 1 1, sector size=512 - WDC WD3200BEVS-08VAT2
Disk /dev/mapper/vg_linuxem64t-lv_swap - 6224 MB / 5936 MiB - CHS 12156928 1 1, sector size=512 - WDC WD3200BEVS-08VAT2
Disk /dev/dm-0 - 313 GB / 292 GiB - CHS 612564992 1 1, sector size=512 - WDC WD3200BEVS-08VAT2
Disk /dev/dm-1 - 6224 MB / 5936 MiB - CHS 12156928 1 1, sector size=512 - WDC WD3200BEVS-08VAT2

Partition table type (auto): Intel
Disk /dev/sdc - 80 GB / 74 GiB - TrekStor DS microdisk q.u
Partition table type: Intel
Partition table type (auto): Intel
Disk /dev/sdc - 80 GB / 74 GiB - TrekStor DS microdisk q.u
Partition table type: None

Analyse Disk /dev/sdc - 80 GB / 74 GiB - CHS 9729 255 63
Current partition structure:
P Unknown 0 0 1 9729 80 63 156301488

search_part()
Disk /dev/sdc - 80 GB / 74 GiB - CHS 9729 255 63

HFS magic value at 164/60/44
part_size 2418422708
HFS 164 60 44 150704 22 45 2418422708 [&çH7-þ*œì®ŠýyV~ØèšàT]
HFS, 1238 GB / 1153 GiB
This partition ends after the disk limits. (start=2638483, size=2418422708, end=2421061190, disk end=156301488)
Disk /dev/sdc - 80 GB / 74 GiB - CHS 9729 255 63
Check the harddisk size: HD jumpers settings, BIOS detection...
The harddisk (80 GB / 74 GiB) seems too small! (< 1239 GB / 1154 GiB)
The following partition can't be recovered:
HFS 164 60 44 150704 22 45 2418422708 [&çH7-þ*œì®ŠýyV~ØèšàT]
HFS, 1238 GB / 1153 GiB

Results

interface_write()

No partition found or selected for recovery

Interface Advanced
P Unknown 0 0 1 9729 80 63 156301488

TestDisk exited normally.
---------------------

Palimpsest Utility recognized the drive, but just will not let me do anything with it except format it.

How can i repair the partitions and MBR without losing all my data?

Any ideas ?

Thanks

Well, this is quite a pickle. Of course, you backed everything up, yes? So there's no chance of losing something important. Yes?

Assuming the above (if it isn't true, stop reading now), boot from a rescue CD or DVD and run "fdisk" on the affected drive. Re-enter the same partition information as when you installed the drive -- you did, of course, remember to write down the partition sizes and locations, yes?

The idea of this rescue method is that you re-enter the lost partition information, but you don't reformat the drive. If you don't have the original partition information, then you have a big problem.

The backup drive is the one quitting on me... did not think of backing up the backup... figures...