ExaGrid, a US start-up, has announced its grid-protected storage concept, in which a grid of storage servers act as a single logical repository. This repository functions behind NAS filers and data is migrated automatically, using user-settable policies, off the filers and into the disk-based repository. Data on the filers is continually backed up to the repository.

Should disaster strike then the NAS filers can be restored at disk-speeds. ExaGrid maintains that backup is 100 per cent reliable. ExaGrid president Jim Pownell says, "Backup to tape is still plagued by issues of lack of data integrity, poor management, instability, and offsite vaulting that makes the tapes inaccessible for immediate recovery should disaster strike."

A repository can be duplicated offsite to provide assurance agaunst repository data being lost. The storage servers in the repository don't have a conventional file system. Instead files are identified through a unique address, a hash code, derived from their content. This is a form of content-addressable storage. Changes to the files are stored instead of complete fresh copies off the files. The software carries out file integrity checking automatically and restores data that is corrupted or lost, according to ExaGrid. This guarantees, ExaGrid claims, file content integrity and reduced disk space needs.

A repository can be spread across two or more locations, with the storage servers holding multiple copies of data, according to policies, so that data can be recovered across an IP network.

The repository can be used to backup SAN-held data by having SAN data stored as files in it.

The storage servers are Intel Linux machines with up to a terabyte of storage. These are used either for the front end NAS filers or for the repository storage servers.

The filers can support NFS, CIFS and FTP protocols. For customers which use third-party backup applications the ExaGrid system provides disk-to-disk backup facilities. Veritas and Legato products are supported plus Oracle's Recovery Manager.

The ExaGrid product is expected to be available in the first quarter of 2004 and is currently in beta test.

It is a complete and self-contained system and thus best suited to complete instances of storage and not to situations where multiple NAS systems are used.