Virtual Storage on Windows NT

In this story:

Step Toward Maturity
HSM, Virtual Storage and Extending Disks
Is It Live, or is It Virtual Tape?

An explosive demand for storage in the client/server space is shifting emphasis away from traditional storage configurations where host systems map directly to storage subsystems on a one-to-one basis. It’s becoming a virtual world out there, and vendors are rushing to deliver storage solutions that allow IT organizations to provide end users with transparent access to corporate data, regardless of its physical location or underlying network topologies.

With storage demands escalating, IT managers need scalable and manageable storage design, says John Bernardi, marketing director for storage resource management products at Veritas Software Corp. ( Virtual storage -- or storage resource management (SRM) -- may be the solution.

SRM is a new strategy in the Windows NT arena, and one that currently suffers from a deficiency of adequate tools, adds Tom Rose, a product marketing manager at storage software vendor HighGround Systems Inc. ( "I have a saying, ‘NT storage is doubling but your IT managers aren’t,’" Rose says. "I’ve seen cases where IT managers spend much of their mornings mapping drives to ensure free space."

Microsoft Corp. has entrusted the problem of developing a storage management infrastructure for its Windows NT operating system to a network of third party vendors. Veritas and HighGround Systems, in particular, offer SRM solutions that enable virtual storage on Windows NT 4.0. Veritas’ Storage Manager version 1.0 and HighGround Systems’ Storage Resource Manager version 3.0 compensate for NT’s SRM deficiencies and enable virtual storage.

"What these [SRM] products do is to take all of these disparate storage resources across a network and collect them and put them into context for you," Rose explains. "They really provide an abstraction layer that takes logical resources and marries them to an existing physical topology."

"Storage Manager offers one management paradigm across all of the resources in an environment, so that you can manage all of the storage resources across your network," Bernardi says. According to Bernardi, Storage Manager’s cross-platform extensibility makes it easier for administrators to deal with capacity management and storage analysis problems across an entire network -- beyond the specific platform on which a particular SRM product is deployed.

Despite having the potential to increase manageability across the heterogeneous systems that compose many enterprise IT environments, most SRM solutions directly benefit only the physical systems on which they’re deployed. Version 3.0 of HighGround Systems’ Storage Resource Manager, for example, can manage only Windows NT servers and workstations, and needs a HighGround SRM agent component installed to do so. This platform-specific limitation is one of the major drawbacks of the SRM world.

The Veritas Storage Manager is an exception. It provides storage management across both Windows NT and Unix environments by allowing administrators to manage both Windows NT and Unix NFS file shares from a single administrative console.

In another exception, an SRM technology residing on one system -- in this case a System/390 mainframe from IBM -- can be of service to both Windows NT and other systems. IBM Cross Platform Extension, a SCSI-to-ESCON disk storage gateway, enables Windows NT and Unix data to be stored and managed on S/390 RAMAC Virtual Arrays.

"In this context, the 390 software sees all of the data that resides on the RAMAC Virtual Arrays and manages all of this data in the same way that it manages native mainframe data, whether or not it’s Unix or NT data," explains Mike Harrison, director of marketing in the storage systems division at IBM Corp.

A vanilla Windows NT installation provides no such virtual storage or SRM facility. For some users, Windows NT presents yet another challenge that stems from Microsoft’s roots in MS-DOS: Windows NT can directly support only 26 drives or storage subsystems, equivalent to the number of drives that can be mapped to the letters of the alphabet.

SRM Technology in Practice

SRM technology has been a boon for Helen Flanagan, an NT project leader with the office supplies chain Staples Inc. ( Flanagan's office is in the midst of migrating data from a number of distributed servers and consolidating it on several larger servers. Flanagan is using HighGround Systems’ Storage Resource Manager 3.0 to help with the transition. By her account, Storage Resource Manager is making storage consolidation easier because it provides her with an instant view of the storage resources in her environment and complements that view with detailed storage analysis and capacity projection reports.

"It keeps track of changes because it renders [all storage resources] in one visual shot, so you don’t have to go to every system and run your reports and consolidate," she explains. "Because we are changing or architecting a lot of the servers, you can really get analytical and start looking at how many files, the size of files, the number of files over a predetermined size-limit."

Storage Resource Manager’s view of networkwide storage is easier to manage and maintain than vanilla NT’s physical one-to-one mapping topology, Flanagan explains. "We really use [Storage Resource Manager] to give us an instant view of everything so that we don’t have to go to each box and to see what’s going on," she notes.

More than anything else, however, SRM technology is helping to ensure that Staples’ business continues to operate without interruption. This was an important consideration, Flanagan says, because the process of server consolidation makes it difficult to track the migration of the data and account for its location when required by end users or applications.

A Maturing Process

Virtual storage on the Windows NT platform is a process undergoing maturation. The maturation is expected to get a boost with the arrival of Microsoft’s Windows 2000 operating system. Windows 2000 is slated to include SRM components -- engineered by both HighGround Systems and Veritas -- that will provide NT with robust storage management services on par with Unix offerings. As part of Windows 2000’s comprehensive storage services, Veritas is expected to provide a logical disk manager service, an NT-native tool similar to the Logical Volume Manager found on many Unix platforms; HighGround Systems will provide a management service for removable and hierarchical storage management devices.

"For the first time in the Windows NT operating system there will be a standard way to manage removable storage, and a standard way for backup applications and tape libraries to interface with the operating system," says HighGround Systems’ Rose. "Windows 2000 will be the first operating system to have a standard interface with removable storage."

Although Windows 2000 will ship with native SRM functionality, IT managers who want a comprehensive SRM solution may still be compelled to use third-party solutions. This path would be consistent with the way IT managers in Unix environments have traditionally handled vendor-supplied SRM tools. They often rely on third-party products to complement and extend the vendor-supplied SRM tools.

Most SRM vendors, however, contend that organizations that need to deploy SRM technologies shouldn’t wait for Windows 2000 when solutions are already available.

Windows 2000, they say, will still lack the ability to manage storage resources in non-Windows NT environments. Windows 2000 SRM will also lack the sophisticated reporting and capacity analysis tools that are part-and-parcel of third party solutions. "The caution [for IT organizations] is to look for [an SRM solution] that is very extensible and feature-rich to make sure that the technology they choose is going to be able to handle whatever [storage] orientations they go with going forward," maintains Veritas’ Bernardi.

HSM, Virtual Storage and Extending Disks

Before there was virtual storage on Windows NT, there was Hierarchical Storage Management (HSM). In concept, HSM had a lot of promise, particularly when the cost of disk storage was five-times today’s relatively low cost per megabyte. But HSM was an idea that never reached its potential.

Today HSM is a term the vendor community uses with great caution. But that’s not to suggest that the concept behind HSM is no longer valid. "When we start talking about HSM, the glaze goes over the IT [manager’s] eyes," laments Jerry Held, vice president of enterprise data storage management products at OTG Software ( "We don’t even talk about HSM, we talk about automated data management."

OTG has built a business around a product called DiskXtender, which extends the virtual size of disk volumes using an abstraction technique that moves files off of a primary disk onto a secondary storage device. Using DiskXtender, an IT manager can specify when files are physically moved from disk to the secondary storage media -- such as tape, optical disk or storage server -- based upon a variety of criteria including age, file size, creation date and last access date.

Held says that a user’s space is limited only to the amount of storage, on any medium, that exists on the network. So a given end user, for example, could be allocated a DLT 7000 cartridge that would provide 70 GB of storage, but it would appear to that individual that they actually have a huge disk allocation that was 70 GB in size.

DiskXtender uses what the company calls a "spy filter driver," which sits at the kernel level and monitors all input and output activity. "When there is I/O activity, it goes through our filter driver," Held explains. He quickly adds that OTG does no modification to the NT kernel, but in Held’s words, "we’re more or less adding to it." When the filter driver intercepts a request for a given file, if the file is not present on physical disk, the request is automatically remapped to the current location of the file. That location is determined by information associated with the file name that remains on the original disk, creating the illusion that the rest of the file is still there, too.

DiskXtender is available directly from OTG software, but it also is integrated into other products, such as NetWorker from Legato Systems Inc. ( --Al Gillen

Is It Live, or is It Virtual Tape?

Virtual storage paradigms are affecting the tape backup marketplace. Virtual tape, a technology in development, is a backup schema in which data is buffered to a physical disk before migration to the tape environment.

"What virtual tape does is basically use a server like a cache before it writes it to tape," explains Brian Adkins, product marketing manager for tape systems at Artecon Inc. ( "One of its biggest advantages is that you can have more logical tapes and logical tape drives than are physically present, but because of the expense involved with the physical media, virtual storage is more often used for mainframe systems where you’ll have big silos of tape libraries."

Traditional tape backup approaches, sometimes use as little as 10 to 20 percent of a tape cartridge. Virtual tape is expected to remedy this problem by improving tape cartridge utilization through volume stacking -- where a number of backup volumes are stored in a physical media buffer and then grouped for migration to the tape medium.

Virtual tape proponents say the technology will bring the functionality of technologies such as hierarchical storage management (HSM) to the tape backup realm. "Virtual tape is kind of like HSM, but actually even more intelligent," Adkins contends. "It will vary the implementation of what gets migrated off and what stays in cache, so there’s even more intelligence involved there."

Although the promise of virtual tape is exciting, it is a promise that has been restricted to mainframe environments due to cost and complexity issues.

"Virtual tape is more well-defined in the MVS environment than anywhere, because that’s an environment where tape is used for many things other than backup," says Linda Higdon, director of Nearline marketing at storage vendor Storage Technology Corp. (

This could change, however, as StorageTek develops a technology in conjunction with Compaq Computer Corp. called Virtual Storage Manager (VSM) to use with StorageTek's Nearline family of tape libraries. "We have a partnership with Compaq Corp., and as part of that partnership what we’re attempting to do is create a virtual tape server for the NT environment," Higdon explains.

Higdon explains the StorageTek/Compaq virtual tape server will present itself to the Windows NT operating system in the form of a DLT tape drive. At the same time it will integrate the level of functionality traditionally provided by virtual tape solutions on mainframe systems. "What the user thinks he has created as a tape volume will actually be directed first to a disk buffer, and then directed to tape on the end," Higdon explains.

StorageTek won’t commit to a delivery timetable for an NT version of its VSM technology, which is currently shipping for mainframe environments. --Stephen Swoyer

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