Hi,
It means that the drive is only partially recognized... It is recognized only as "Unknown"...
The Unallocated indicates that Windows thinks that the drive is blank, or empty, with no partitions...
I would try running chkdsk d: /r where d:\ is replaced by the drive letter of the drive you want to check...
The problem is your's does not have a drive letter...
You might try accessing the "Properties" of the drive in Disk Management and see if CHKDSK is available under the "TOOLS" tab...