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Modernize mainframe storage

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Market pressures and new technologies are pushing the world of the mainframe and open systems together. Here's how:
FICON, at 100MB/s, offers a faster replacement for 17MB/s ESCON interconnects and provides compatibility with Fibre Channel (FC) storage area networks (SANs) as well as the ability to span much longer distances.
New storage management systems address both mainframe and open systems storage through a single interface.
Hierarchical Storage Management (HSM), used for decades on mainframes, is becoming common in open systems environments as tape and slower nearline disk arrays move lesser-used data away from primary disk.
Storage experts skilled in the mores of expensive mainframe storage are imposing tighter restrictions on their users than space-hungry open systems administrators.
IBM's Linux on the mainframe provides the logical benefits of an open systems environment--such as a native SCSI stack--while retaining the large-scale benefits of the mainframe, such as the ability to run thousands of virtual servers.

However, there are more than a few reasons to hold onto your mainframes:
Group-based storage policies automatically constrain user resource access, and open systems storage usage tends to mushroom over time.
Mainframes offer a more highly granular security model with no root access or other vulnerabilities that plague open systems.
Open systems are the lowest common denominator for multiplatform management tools--the more mature management capabilities of the mainframe are compromised, unless mainframe-based tools are retained.
Older mainframes are victims of their own proprietary design. Those based on VSAM structures, for example, will have trouble moving to modern block-based storage.
The lack of mainframe driver support means vendors are slow to support new open systems technologies and provide integration with SANs.
We're always looking for faster ways to back up data," says Diane Iñiguez, director of enterprise storage management within Marriott's Information Resources division, in Frederick, MD. Next year, the constant quest to improve backup and disk performance will result in Marriott's modernizing its mainframe storage environment, rather than following fashion and switching to open systems.

"The structure and management processes are very sophisticated in the mainframe environment, whereas open systems are still in their infancy and trying to catch up," Iñiguez says (for more on Marriott's project, see "Marriott stays with mainframe storage").

John Herbert is another IT manager who never got the message that the mainframe is dead. As storage management supervisor with New Jersey's Office of Information Technology, Trenton, NJ, Herbert directs the strategy for the more than 11TB of storage used by the IBM mainframes supporting most of the state's government departments. Mainframes aren't only alive and well under Herbert's watch--their use is growing as many applications are moved from open systems, back onto more reliable multiple virtual storage (MVS).

That goes against the conventional wisdom mainframes are simply a legacy platform and mainframe-only storage should be folded into omnipresent, multiplatform storage area networks (SANs). Call him an old fuddy duddy, but Herbert's three-person team maintains a separate 7TB compressed mainframe and 4TB open systems SANs, and so far he remains unconvinced that consolidation is a step in the right direction.

"You manage [mainframe and open systems storage] differently and maintain them differently," he says. "I can see the advantages of consolidation, but I don't see us taking advantage of it. Some of the basic stuff is a problem, like dynamic sparing and the nightmare of root security [on Unix]. The mainframe is still a long way from the server as far as disaster recovery capabilities."

Rather than pushing storage onto what are effectively open systems storage arrays with mainframe interconnects, Herbert is using the mainframe as the state's primary data management tool. Open systems servers may stick Web interfaces on top of key Customer Information Control System (CICS) databases, but the data remains safely stored on a Hitachi Data Systems (HDS) 9960 storage array that was recently installed to consolidate several slower, smaller direct-access storage device (DASD) systems.

Everywhere mainframes are used, storage administrators are finding out that despite years of grandstanding by open systems vendors, the advancing pace of technology has not left the mainframe behind. Their market penetration may be dropping--from 13% in 2001 to 8% in 2006, according to IDC--but the downward trend may be more reflective of a growing market than of mainframes' lack of popularity.

Indeed, mainframe-attached storage still accounts for a major proportion of the sales of EMC, HDS, and IBM, which together account for the bulk of mainframe-attached storage systems. Mainframe users are clearly making the most of their investments, and are continuing to add to their storage pools as their mission-critical applications grow.

Aiming to bring those mainframes up to scratch with their fast-moving open systems cousins, mainframe storage vendors have breathed new life into mainframe storage by bridging the gaps between flexible open system SANs and legendarily robust and mature mainframes.

The new ESCON
Foremost among these improvements is FICON, a mainframe interconnect introduced by IBM in 1998, but still in the planning stages at most companies. FICON bundles the equivalent of eight ESCON channels--each of which can support up to 4,000 I/O operations per second--into a standard fiber connection. The result is full-duplex data transfers of up to 100MB/s, compared with just 17MB/s half-duplex data transmission in ESCON environments and 4.5MB/s using old parallel technology.

Architecturally, FICON is similar to Fibre Channel (FC), which has become the standard method for interconnecting storage and servers within open system SANs. Four out of five layers in FICON and FC are identical--the only differences are in their top layer signaling. This allows compatibility with existing FC equipment, which is a significant benefit because FICON allows mainframes to be easily linked with a broad range of FC-capable servers, storage arrays, tape drives and other SAN-related equipment.

FICON also offers better error correction than ESCON, and supports up to 16,384 unit addresses per channel compared with ESCON's 1,024 unit addresses per channel.

Seamless connectivity is an underlying requirement for the integration of mainframes into evolving SANs, yet it's not the only reason FICON is winning supporters. For many companies, FICON's most appealing trait is its ability to maintain data integrity over much longer distances than was possible with ESCON (over 20 km without repeaters and 100 km with repeaters, as opposed to ESCON's maximum of three km without repeaters and 43 km with repeaters). Boosted by EMC's Multi-Hop technology, FICON has been extended thousands of miles across the Atlantic.

The extra distance provides much-needed flexibility in the design of disaster recovery strategies, allowing companies to set up continual data replication policies between primary and secondary data centers. Using remote replication features of the mainframe-attached storage, data consistency and integrity become far easier to guarantee.

This was first published in February 2003

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