Some vendors advertise enterprise automated tape libraries (ATLs) that support multiple platforms, but they don't support all platforms. Because of technical limitations, users deploy ATLs to support Unix servers or mainframe-hosted applications, yet they don't connect the two platforms to the same ATL. What's needed is a single enterprise tape environment that supports legacy and open platforms. But there are a number of reasons why cross-platform tape support is neither widespread nor well-exploited.

Enterprise disk arrays can be easily shared across platforms. But some observers believe tape vendors have gotten off with barely a slap on the wrist for not enabling their products to connect to all of the platforms in the data center. For example, the Storage Networking Industry Association (SNIA) has developed a standard model for shared storage, but barely addresses cross-platform ATL sharing.

				Do IP networks make tape sharing easier?
				One of the factors contributing to the widespread adoption of NAS is multiprotocol file sharing over common networks. There's no NAS equivalent for tape drives, although some analysts have advocated IP storage networking as a means of making tape consolidation easier. The emergence of IP-based storage has many benefits to storage environments. Multiprotocol file sharing over common networks has accelerated the drive toward cross-platform support. Conversely, IP access to tape drives has been slow to develop primarily because of the performance implications posed by the nature of tape mounting and writing. In other words, when a tape drive isn't continually mounted and/or data rates aren't constant, it "shoe-shines" and is forced to reposition itself, thereby imposing a significant latency penalty. This problem worsens with faster drives because it's even more difficult for backup infrastructures to keep them close to rated throughput. Variable speed matching helps to some extent, but doesn't provide enough benefit considering the unpredictable delivery rates of IP networks. Unfortunately, IP networks are unable to overcome the deficiencies of tape when it comes to host multiplatform resource sharing.

A recent SNIA presentation, "Tape in SNIA's Shared Storage Model," described methods for tape drive sharing, access and virtualization. Whether discussing LAN- or SAN-attached tape drives, Network Data Management Protocol NAS backup methodology or even newer Xcopy techniques for serverless backup, SNIA doesn't address cross-platform support.

Multiplatform support for ATLs is costly and complex. IBM Corp. offers the 3494 ATL, but it's rarely used for simultaneous Unix, Windows and mainframe connectivity; to do that, the library drives and slots must be physically and logically partitioned with no resource sharing.

Storage Technology Corp. (StorageTek, now owned by Sun) uses a similar approach with its Streamline SL8500, PowderHorn and TimberWolf ATLs, which have multiplatform support but are configured to support mainframes or open systems. For cross-platform sharing, a variety of software is needed, including Library Station, ACSLS and Gresham EDT-DistribuTape.

Simultaneous support for mainframes and open systems is difficult, but users can achieve some ATL sharing between Windows and Unix platforms. But even this basic sharing is a function of backup software or an intermediary device. The backup software (for example, Veritas' Shared Storage Option, now owned by Symantec) or device (for example, IBM's Virtual Tape Server [VTS] or StorageTek's Virtual Storage Manager [VSM]) controls access to the robot and associated drives, acting as a traffic cop so that no two tape mounts are made to the same drive at the same time by different tasks.

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