Mount disk

Hi,

my senario is  i have an external usb hardisk to take backups when i trying to mount it 

it doesnt mountig i use command

#mount /dev/sdd1 /media/backup_disk

and i notice 1 thing is that my filesystem drives automatically converted to logiacl partition when i raise command

#df -h

its show me filesystem is logical .How it can convert to logical automatically.

i couldnot able to mount the backupdisk and i cehck the backupdisk on diffrent machine its working good.