HDD: Western Digital My Passport Essential SE 1TB (2.5 ")
The dimensions of the hard drive are: 11 cm x 8,5 cm (length x width)
Of width, the disk has fitted perfectly, but also had no room, so your HDD should not be wider than 8.5 cm.
The problem was the length with me. Inside the bag there are 2 straps that hold the hard drive in the interior in place. For me it did not work because my hard drive is so short that the 2 belt ranreichen just barely on the two outside edges, consequence is that the belt slip and the hard drive is no longer detained. Therefore, I recommend you this bag only to buy if your HDD is at least 13 cm long.
My overall impression was of his pocket but very good, so I pulled off only one star because of poor size information.