A harddrive can store large amounts of data and without you needing to install games on your harddrive before you can run them the small 60 Meg harddrive will last everyone.
The harddrive itself is a standard 50 Pin SCSI drive which can be changed for a larger drive if needed. (But my Amiga 4000 has just over 1.1Gig and that is loaded with lots of games, Every picture of the CDTV I have ever come across (Plus three versions of this CDTV site and two versions of the Marina website and four Mpeg films), In comparison the Marina`s PC has a 4.5Gig drive and its 92% full with the OS totaling more than 2 Gig.)
The harddrive is specially styled by Commodore for the CDTV (For once its not a black version of another Amiga unlike the Keyboard, Diskdrive, monitor, Etc..), Its basically looks like a large harddrive (With a circle where the drive`s disk platter is).

The connector on the back is a standard SCSI 1 connector (Looks like the end of a printer cable).
The card is Commodore`s standard SCSI interface with a 25 Pin external connector (Available seperatly for £50).
The drive cost £219.99 when new (In 1993) when the CDTV only cost £229.99, With that in mind you will guess that there are not many of these around, Infact I have only seen three in ten years, You will be very lucky to find one of these now and I have never seen one in a box or with a manual but they should have come with both of them.