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Using a LAN as a transport carrier, most backup products move data directly from the disk being backup to some sort of an external tape-based backup device. Systems administrator will agree about one thing -- the low cost per megabyte of tape has become the most cost effective way to keep many gigabytes of data on the shelf in case the primary disk storage failed, or the copy of the data got lost.
Unfortunately, even today's speed demon tape backup devices run no faster than about 15 megabytes per second. When the fastest possible LAN connection to that device equals the same speed, 15 megabytes doesn't seem so slow. On the other hand, with the use of SANs capable of nearly 100 megabytes per second and disk subsystems capable of nearly the same speed, the slow speed of tape backup devices has become the bottleneck to both backups and restores. To eliminate the bottleneck and to take advantage of the failing prices of disk storage, organizations have started to backup across the SAN from online disk storage to offline disk storage before migrating to tape.
Ironically, the majority of restore requests from backed up data include files that are less than a few days old. If the most recently backed up data resides on an offline disk storage for a few days before the data gets moved to tape, then the majority of retrieval requests would be fulfilled at disk speed, not tape speed. To this end, the restored data doesnt have to come off at 15 megabytes per second tape. Instead, the restored data can come off an 85-megabytes per second disk subsystem. SAN file sharing software, such as Tivolis SANergy running on all the computers connected to the SAN allows any computer to both backup and retrieve files from this offline disk storage at SAN speeds. Because SAN file sharing software makes this offline storage appear to be across the LAN, any backup and restore program capable of using disks across a LAN can instantly realize a 20 times speed increase in both backups and restores. Essentially, sharing software enables both LAN-free and application-serverless backups and restores without requiring special backup software to do so.
SAN file sharing software uses the maturity, security, and inherent sharing abilities of industry standard LANs and enhances them with the guaranteed delivery, high bandwidth and low processor overhead of SANs to provide high-performance file and file system sharing between multiple operating systems connected to a SAN.
SAN file sharing software runs on many different operating systems to provide transparent cross-platform sharing at SAN speeds from storage formatted with just a single industry-standard file system. It eliminates the one-to-one relationship between disk volumes and computers by allowing multiple computers to share single disk volumes, greatly simplifying storage administrator and reducing costs.
Elizabeth M. Ferrarini She is a free-lance writer from Boston, MA