Tape SAN for Dynamic Drive Sharing

Resource Optimisation

Addressing backup throughput and LAN congestion issues with simple, SCSI-based tape library sharing quickly becomes expensive: one or more tape drives must be dedicated to each host with a large volume of data for backup. The tape drives are then under-utilised as they're only needed for a couple of hours during each full backup. Dynamic drive sharing on a tape SAN is a solution to this problem that's rapidly becoming the defacto standard approach.

Tape Drive Sharing

Advantages

• Cost savings from more efficient use of tape resources - As tape drives can now be dynamically reassigned to where they're needed most, fewer tape drives are required in total. This means savings in both purchase cost and ongoing hardware maintenance.
• Cost savings from deferred tape library purchases - With fewer tape drives required, it is less likely that an additional tape drive will be required purely to house additional tape drives.
• Improved backup and recover times in an emergency - In a critical situation, most or all of the SAN-attached tape drives can be made available to a single server for very rapid backup or recovery.

Disadvantages

• Initial cost of SAN infrastructure - Tape SANs deliver very good return on investment, but naturally require an up-front expenditure to put the infrastructure in place. However, the cost of SAN infrastructure is falling rapidly as the technology becomes more widely accepted in the marketplace.
• Increased complexity - SAN connected, dynamically reassigned tape drives require much more careful configuration and management than tape drives that are SCSI connected and dedicated to a single server indefinitely.

Another strategy for avoiding LAN congestion is to implement a dedicated backup LAN. This approach has pros and cons, but is worth considering even if it's in conjunction with other strategies (such as a tape SAN).