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The fruits of all this work will become evident when Windows .NET Server finally debuts next year. The launch will be crunch time for Microsoft's recently formed Enterprise Storage Group (ESG) - headed by Microsoft senior vice president Bob Muglia - which will play its hand by introducing several storage-related .NET features that should improve Windows' still-developing storage credentials.
At the core of ESG's storage management plans is the Virtual Disk Service (VDS), a Windows .NET Server component that provides block-level virtualization of stored data. VDS includes a host of APIs that let applications manage those blocks with high granularity and control. Using these APIs will give storage management applications better control over file system operation. Although VDS interfaces will remain somewhat vaguely documented at first, Microsoft promises the first update to Windows .NET Server will fill in VDS documentation gaps.
VDS's major claim to fame is its promise to simplify the management of multiple elements within the storage infrastructure. According to Keith Hageman, U.S. program manager for core file services, VDS will
In addition, a utility called Diskraid will ship with the .NET Server resource kit that will allow granular control of which spindles will be used by a given LUN. Microsoft claims that Diskraid and VDS will simplify the process of writing scripts to control various processes on different vendors' arrays, since VDS will abstract some of the hardware-specific details.
Most anticipated among the new features is Volume Shadow Copy Services (VSS), a service that builds on VDS to provide instantaneous, full or incremental backups of chosen NTFS volumes or specific applications. Data is dumped into a file, and the mirrored application is free to resume operation. VSS files can then be backed up onto locally-attached tape or disk, or sent to another dedicated server for archiving - without increasing the CPU load on the primary server. Microsoft's design goal is to support multivendor snapshots with a total application downtime (freeze to thaw) of less than 10 seconds.
The VSS architecture consists of writers and providers. VSS providers, which receive snapshots and store them, are embedded in management applications such as NTbackup or third-party systems. Providers get their data by communicating with writers embedded in each target application. Once a signal is received, the VSS writer initiates actions such as freezing a database while the snapshot is taken, resuming its operation afterwards and confirming the snapshot was taken correctly.
One thing VSS promises to do, at least for the Windows world, is bridge the gap between backup software packages, application-specific backup modules, and device-specific snapshot capabilities. VSS-enabled backup software would automatically be able to backup any application with VSS writer on any device with a VSS provider (see "VSS simplifies application backup"). With backup software support from some of the majors (Veritas and Legato, for example) and hardware support from EMC, HDS, HP, and XIOtech as of this writing, many users would have the potential of simplifying backup of key applications.
Windows .NET Server will ship with writers for Active Directory, NTFS file systems and SQL Server. Microsoft and third parties will work to develop other VSS writers for specific applications. This approach gives storage administrators a high level of control over specific backup operations and let ISVs develop specific tweaks to optimize interaction with particular applications. For example, a custom VSS writer might provide advanced archiving of Exchange e-mail systems, allowing better long-term management of e-mail communications as mandated by recent SEC policies. In fact, Microsoft says, the Exchange writer will be part of the next version of the e-mail server (now code-named Titanium).
Adding snapshot capabilities to .NET Server will help Microsoft slowly inch into the high-end storage management area it wants so desperately to inhabit. The company has already won over major ISVs by offering its shadow copy methodology as a consistent standard for data imaging. This is a major sweetener for ISVs that have traditionally had to develop their own proprietary snapshot technology.
"In the past, if a vendor wanted to make functionality like this available on Windows, they had to write a complete solution," says Eric Burgener, senior director of platform strategy with Veritas. "Now we'll be able to make system calls into .NET, which means it's going to be that much easier to provide these features in Windows."
VSS is about more than backup, however. Because it's tightly integrated with NTFS, VSS allows administrators to give users live access to old snapshot images. Shares on Shadow Copy folders operate just like any other volume. For example, with Shadow Copies for Shared Folders, users can directly access old versions of their files through a Windows Explorer-like interface. This capability is available today for XP users.
"Users with [Shadow Copies for Shared Folders] enabled can see old versions of files, and they're managed just as they would manage ordinary files," says Jason Goodman, product manager for storage technologies in Microsoft's Windows .NET Server Solutions Group. "This allows for user-initiated undeletes of previous versions of files. Imagine this as an enabling technology for HSM-like near-line storage capabilities. Because it's enabled through the file system, it's transparent to the user."
Administrators of Windows .NET Server systems configure VSS through the Disk Management or Shared Folders Snap-Ins within the Computer Management console. The amount of disk space dedicated to shadow copies is set by the administrator, with older images automatically deleted as necessary to free up space for new snapshots.
Sharing restrictions have meant Windows NT and Windows 2000 Server lack the ability to back up open files currently locked for use by specific end users; such files are unceremoniously skipped during backup. Within .NET Server, however, VSS will allow backups to archive works in progress by backing up even open files; unsaved but backed-up versions will be available to users alongside old versions of properly saved files.
This was first published in August 2002