Ian Watkins database 27 terabytes.
 

The computer storage seized has a capacity of 4 or 5 times the size of the complete database of the South Wales Police.

No idea who Ian Watkins is .... but if one guesses it could be something involving high resolution videos and images, it might not take long to reach 27 terabytes .... the South Wales Police database is probably largely text with a limited amount of binary data (they are probably not counting the size of the South Wales Police email system either).

Also consider some of it may be backup drives etc.

In this day and age, 27 terabytes is not particularly impressive and can be had relatively cheaply (cheapo 1TB drives for home users can be had for £50 each... buy two or three a month and before you know it you have 27TB.... cheap 4TB drives running at £130 each and you'll get there even quicker) ...... petabytes and greater are more interesting !

Obviously not condoning any reported criminal activity ... just talking here in pure technical terms about the pace at which videos and photos eat up space !

Explanation for those unfamiliar with the case.
 

Seems that the guy was into encryption, too . . .

. . . but GCHQ cracked his passwords . . .

BBC News - Lostprophets' Ian Watkins: "Tech savvy" web haul