Sales of disk-based storage systems and storage related elements reached $5.6bn in the second quarter of 2005, up 9.9 per cent year on year.

Vendors shipped 59.3 per cent more storage capacity reaching a total of 457 petabytes, according to newly published research from IDC.

A petabyte is one million gigabytes. The books in the US Library of Congress contain about 20 terabytes of text.

HP held on to the top spot in the overall market for disk-based storage systems with a 23.4 per cent market share, followed by IBM at 20.5 per cent and EMC at 14.4 per cent.

EMC held on to its lead in the external storage market, growing sales by 9.6 per cent to reach an overall share of 21.2 per cent. HP and IBM followed with 18.8 and 13.8 per cent respectively. Dell, HP and IBM accomplished strong growth relative to last year's second quarter.

Three of the top five vendors enjoyed double-digit growth during the second quarter. Dell led the way with 27.1 per cent year-over-year growth followed by HP and IBM, each with more than 13 per cent.

Many vendors sell co-branded hardware that clouds the market share picture, however. Dell sells hardware made by EMC, and Sun and HP have OEM agreements with Hitachi for storage hardware.

In the market for network attached storage, EMC and Network Appliance held on to most of the sales with 40.2 and 35.2 per cent market share respectively.