OS X can't unmount disk My 1TB LaCie Rugged THB decided it was a good idea to stop working all of a sudden.
If I open it in disk util I sometimes see an actual name of a partition, but most likely it's not the real name.

In Terminal I tried:

diskutil list
/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *251.0 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                  Apple_HFS Macintosh HD            140.0 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
   4:       Microsoft Basic Data BOOTCAMP                110.1 GB   disk0s4
/dev/disk1
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *1.0 TB     disk1
   1:                  Apple_HFS                         150.1 GB   disk1s1
   2:                 DOS_FAT_32 BAK_WIN                 150.0 GB   disk1s2
   3:                  Apple_HFS                         100.0 GB   disk1s3
   4:                 DOS_FAT_32                         120.0 GB   disk1s5
   5:                 DOS_FAT_32                         480.1 GB   disk1s6


And then to unmount this:

$sudo diskutil unmountDisk force disk1


gave this: Forced unmount of disk1 failed: at least one volume could not be unmounted
Than for each disk:

$sudo diskutil unmount force disk1sn


Always: disk1sn was already unmounted

Because I wasn't able to do anything with my external HDD I made a desperate attempt to erase everything on it, including unbackuped files, cause this used to be the backup plan. This was the try:

$ sudo diskutil eraseDisk JHFS+ DISK_VOLUME disk1
Started erase on disk1
Unmounting disk
Error: -69888: Couldn't unmount disk


But it didn't work as well. If you have any idea to get the HDD working or even safe the files, I would be really grateful.

Almost forgot about this from Disk Utility:
Disk Utility can’t repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed-up files.
For me, none of the solutions were working: sudo unmount, sudo unmountDisk, unmountDisk force, etc., with /dev/disk4, /dev/disk4s1, /dev/disk4s2, and so on. All failed. The last thing I tried - eraseDisk - gave me the same error: Error: -69888: Couldn't unmount disk

Then I decided to see if there were any processes in my way, so I ran sudo lsof|grep disk4 and found a process working on one of my partitions. I killed the process id and suddenly the disk mounted again! Success!