Open Systems Connectivity To Mainframe Storage Networks - excerpt from Marc Farley's book, "Building Storage Networks" - Technology Information

Computer Technology Review, March, 2000 by Marc Farley

This article, excerpted from Marc Farley 's book: "Building Storage Networks ", was reproduced with the permission of The McGraw-Hill Companies. Copyright 2000. Osborne/McGraw-Hill.

IT organizations with both mainframes and large open systems computers have tried to improve the ability to share, transfer, and exchange data between these platforms for several years. The ability to do these things supports new applications that cross organizational boundaries and help integrate corporate policies and decisions. Corporate restructuring around the concepts of ERP (Enterprise Resource Planning) systems such as SAP, Peoplesoft, Baan, and others depends on the ability to share or exchange data among the various parts of the organizations. Doing this sooner, rather than later, is a constant goal to help attain a consistent execution of strategic initiatives.

Historically, mainframes and open systems computing environments have been islands of information with relatively slow links between them using file transfer technology over SNA (Systems Network Architecture) and IP data networks. Functions such as NFS have been available on mainframes but historically have not delivered the performance and capabilities one would expect from them due to fundamental differences in machine and network architectures between mainframes and open systems machines.

The phenomenon of the Internet has helped change this scenario as mainframe systems have seen rapid development in Internet protocol handling technology. It remains to be seen how effective the results of these development efforts will be. System, software, and hardware vendors have been touting the ability to integrate mainframe and open systems technologies for many years, but the fact is there is a long way to go. Storage networks in the form of Fibre Channel and FICON may be able to play key roles in improving the current situation. However, the method of sharing and exchanging data between mainframe and open systems I/O channels is still not clearly defined. This article explores some of the technologies and techniques for transferring data through storage I/O mechanisms between mainframe and open systems computers.

Exchanging Data Across Platforms

The ability to exchange data between mainframe and open systems platforms today is somewhat limited. The discussion in this article does not cover data transfers that occur over TCP/IP and SNA (Systems Network Architecture) networks. As an article about storage networking, such methods of transferring data are not really applicable. Nor do they work very well, due to the fact that they involve both processors and lots of inefficient data network processes.

Instead, we focus here on data transfers that occur over storage conduits-- ESCON and SCSI. While it would be great to say that a lot has been done between ESCON and SANs, the truth is, that has not happened yet. Nonetheless, this article treats the subject as if ESCON to SAN is already a reality, and presents much of the information that way in anticipation of the strong currents in the market in this direction. Three methods that have been developed to exchange data between mainframes and open systems platforms are:

* Storage pooling

* Device emulation

* Data sharing

Storage Pooling Between Open Systems And Mainframes

Storage pooling is a storage management application that aggregates and subdivides disk storage in order to share the raw capacity across multiple systems. Storage pooling can be used to provide storage capacity to both open systems and mainframe computers even though the data structure is considerably different for both machines. A disk subsystem with many devices or the ability to virtual drives can allocate some of its resources for mainframe storage, some for open systems storage, and leave unused resources to be determined. Fig 1 shows a storage subsystem being shared between a mainframe system over ESCON and Unix and NetWare systems over a SAN.

In general, storage pooling does not facilitate data exchanges between virtual devices in a disk subsystem. However, EMC, Hitachi Data Systems, and other companies have developed internal data transfer functions that copy data between mainframe devices and open systems devices within a storage subsystem. This demonstrates some of the potential of intelligent storage subsystems in providing higher levels of data management.

Device Emulation

Device emulation, or virtualization as it sometimes turns out to be, can be used between mainframe and open systems just like it can be used between practically any other combination of systems and devices.

Typically, mainframe storage devices are more expensive than their open systems cousins. Therefore, the ability to implement less expensive open systems devices in place of mainframe devices is appealing to mainframe systems managers who want to implement lower cost products. Not only do open systems devices cost less, but the maintenance and supplies for them also cost less. For instance, magnetic tapes for open systems tape drives tend to be less expensive on a cost-per-megabyte basis than mainframe tape drives.