The disk storage industry defied economic gloom in the second quarter with strong increases in both capacity sold and revenue, according to two research companies.

Worldwide revenue from external disk storage systems grew 16.7 percent in the quarter, the fastest year-over-year increase that market has seen in two years, IDC said on Friday. Meanwhile, total disk storage systems revenue grew 10.9 percent, according to IDC. Vendors shipped 1,777 petabytes of capacity in total, up 43.7 percent from a year earlier.

Sales growth was remarkable especially because it occurred across several market segments, IDC said in a news release.

Despite economic slowdowns in some parts of the world, storage demand has been growing rapidly, driven in part by increased use of video and by regulations that force enterprises to preserve more data. IDC has estimated overall demand for storage capacity is growing by about 60 percent per year.

IDC defines a disk storage system as a set of storage elements associated with three or more disks. Some are located inside server cabinets and some are external. While the total disk storage system market hit US$6.9 billion in revenue in the second quarter, the external market grew to $5.08 billion.

EMC kept its lead in external disk storage systems with 21.7 percent of the market, followed by IBM and Hewlett-Packard in a statistical tie with 13.1 percent and 12.9 percent, respectively. EMC's revenue grew fastest among the major vendors, up 19.7 percent to $1.101 billion from $920 billion a year earlier. HP's growth rate was lowest, at 8.2 percent, and the company lost a full percentage point in market share.

In the total disk storage systems market, HP fared even worse with a 1.2 percent drop in revenue, while all other major vendors gained. Though HP remained in the lead, it fell to an 18.1 percent market share, nearly tied with IBM at 17.7 percent. EMC was in third place and Dell in fourth. Sun Microsystems had the strongest rise in revenue, at 29.2 percent. Its revenue grew to $494 million and its market share to 7.1 percent.

According to figures from research company Gartner, the external controller-based disk storage market grew 18.8 percent in the second quarter, reaching $4.46 billion in revenue. EMC lost half a percentage point of market share but maintained a commanding lead at 24.3 percent, experiencing 16 percent revenue growth in the quarter. Next was IBM with 14.1 percent of the market, followed by HP, Dell and Hitachi Data Systems. NetApp came in sixth but had a strong 22.9 percent revenue gain, Gartner said.