In the out-of-band approach taken by EMC, the process of mapping logical addresses to physical addresses takes place in SAN switches from Brocade Communications, Cisco Systems, and (beginning in 2006) McData. IBM has taken an in-band approach with its SAN Volume Controller, in which the mapping takes place at devices residing in the data path. Other virtualization products, such as Hitachi Data Systems' TagmaStore and Hewlett-Packard's Enterprise Virtualization Array, place the mapping intelligence within the arrays themselves.
Virtualization can better utilize storage resources and eliminate the need to take down critical applications when reconfiguring storage. "Virtualization allows the management of the IT infrastructure to be independent of the management of applications," Mark Lewis, executive VP and chief development officer of EMC, said in a Webcast.
Invista is being targeted initially at large enterprises with at least five to 10 disk arrays, the minimum needed to make virtualization practical, Lewis said. "Those companies have the most complex infrastructures and can benefit the most from a virtualization solution."
IBM was quick to point out that its SAN Volume Controller is in use at 1,000 customers, many of them smaller businesses, and that some features, such as data replication, were missing from EMC's announcement. "This appears to be an extended beta program for EMC's high-end customers in lieu of being able to deliver true disk virtualization," said Tom Hawk, IBM's general manager of storage software, in a statement.
Hewlett-Packard on Monday upgraded its Enterprise Virtualization Arrays with new replication features, including Snapclone, which makes copies of disks for long-term preservation, and Snapshot, which creates short-lived images of disks for backup.