Ibm TS7700 User Manual

High-End Virtual Tape:

IBM Leaps Ahead with a New Grid Architecture

Summary

IBM has invented virtual tape again and far for the better.

Introduction

IBM invented virtual tape in 1996 beating StorageTek, to the market by two years. (Note that Sun acquired StorageTek and all subsequent references will be to Sun in this document).

IBM and Sun dominate the high-end virtual tape market, which has previously been mostly a game of performance leapfrog.

However, IBM recently introduced a dramatically improved architecture and products, while Sun continues to plod along with an old architecture.

Points to Remember

• IBM invented virtual tape.

• IBM’s new virtual tape grid architecture lets virtual

tape data reside anywhere on a virtual tape grid.

• New gigabit IP links are easier to use and cost less

• IBM’s new policy management features make it easy to meet recovery objectives.

• IBM’s new hardware outperforms Sun’s in most cases.

• IBM has fulfilled on its goal to facilitate migration from its older architecture products.

• Sun has lagged behind IBM in replication and FICON support

• IBM is much more open than Sun.

Architectures

IBM

Named the IBM TS7700 Virtualization Engine, this new system is a significant change from the previous architecture. IBM calls this new architecture its “Virtual Tape Grid” and, while it continues to be based on outboard subsystems, the way nodes operate and are managed is totally changed. At its heart, this grid is a move away from a monolithic approach to a more distributed one. Unlike IBM’s old peer-to-peer architecture, the individual TS7700 nodes are managed as an integrated whole. Moreover, each node adds capacity to the local grid and sports new gigabit IP links for inter-node traffic.

Another important architectural difference is that IBM now virtualizes the location and number of virtual volumes. This permits access and recovery from any node and was a key design goal. The idea is to completely divorce the user from having to know where tape data actually resides and how many copies there are. Instead, users can specify recovery policies that will ultimately dictate these. As we discuss below, this added virtualization dimension is not only a big step in supporting business continuity with advanced policy management; it is also a necessary step in content-based access for tape data.

User interest in the new gigabit IP links has been strong as they look for simpler and less expensive ways to replicate tape data. IBM led the market with synchronous replication and has always had asynchronous replication.

Although IBM’s tape grid currently supports three nodes, it has been designed to support at least eight nodes as well as to support future enhancements in cache capacity, performance, content-based access and data de-duplication. It also leverages IBM’s vast array of technologies for performance, encryption and futures.

Playing catch-up, IBM has finally added the capability to export a copy of the logical volumes stored to the node for disaster recovery purposes. Also, IBM’s tape grid is not compatible with its previous architecture, but a wealth of migration tools are available.

Sun

Sun continues to employ a hybrid approach where most of the virtual tape logic sits on mainframe-based software while tape I/O and replication services are handled by a relatively dumb external hardware subsystem based on Sun’s SVA array which is no longer being actively marketed.

In addition, availability features are limited to two-node clusters with no more than four nodes total (one local cluster and one remote cluster) often referred to as a “quadplex”. Worse yet, only one set of channels must handle all I/O (host, tape drives, and remote communication) making it difficult to balance changing workloads. In addition, without gigabit IP links, expensive channel extenders or routers must be used to reach remote sites.

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