Until recently, I didn't pay much attention to Microsoft Remote Storage Service (RSS). However, as more companies consider deploying their Windows servers and applications on high-capacity Storage Area Networks (SANs) and other "storage utility" environments, and as application data continues to bloat, RSS is becoming a tool that Windows administrators can't afford to ignore. Let's examine RSS and consider what it can do for your organization.
RSS: Microsoft's HSM
If you've worked in IT for any reasonable length of time, you know that the promise of Hierarchical Storage Management (HSM) preceded the Windows platform. HSM lets you prune data from total storage to accomplish key goals such as reducing total storage consumption, shrinking backup windows, and migrating unneeded data from local storage.
I've always thought of HSM as a three-tiered approach to data management. Tier 1 is online storage, at which data remains immediately accessible to applications and user requests. This storage includes straightforward nonremovable storage mechanisms such as local hard disks, SAN storage, and application stores. Tier 2 is near-line storage, which is data you've migrated to an intermediate secondary storage container (either removable or nonremovable) in the form of a secondary magnetic disk device, an optical disk device, or even an application-specific storage mechanism. Tier 3 is far-line storage, which is data that you've migrated to a removable storage device such as tape or other media for later use and recovery.
What drives HSM products is the need to segment data stores into context- and time-sensitive containers of manageability. For example, as a Microsoft Exchange Server administrator, I can try to work with a monolithic mass of data that continually frustrates me and leaves me feeling helpless, or I can implement a data-management strategy that includes HSM to gain control of that data. If I'm a Windows administrator managing a file server with terabytes of data, I can manage this data as one set or approach it as several subsets—for example, frequently used, rarely used, and never used data. I can then decide whether to include policies for each subset of data (e.g., back up frequently used data every night, migrate less frequently used data to tape). These features are the essence of HSM technology that many enterprises are beginning to think about in the Windows space.
Microsoft introduced RSS, its implementation of HSM, with Windows 2000. However, RSS is simpler than HSM in that it differentiates between just two levels of storage—local and remote. As a result, RSS migrates data transparently from local disk storage to remote devices such as tape libraries.
The Win2K Server OS includes RSS, and computers running Win2K Professional are also HSM-aware. Many elements of the storage, application, and GUI are HSM-aware and work together to ensure that HSM integrates fully into the user experience.
What Remote Storage Buys You
Some of RSS's benefits are immediately obvious. The concept of managing data files from primary storage paves the way to cost savings by limiting storage growth (or at least flattening the growth curve), which sounds good to administrators—especially when it requires little intervention on their part. You can encourage users to store data on file servers so RSS can manage that data according to its use. Local-server storage becomes the primary place for frequently used files, and infrequently used files can go elsewhere. The idea is to have data reside on the most effective media according to the data's usage profile (i.e., frequently or infrequently used). You can base policy-driven file migration on file size, last-access date, and custom inclusion and exclusion rules.
To users, files in local storage appear much as they did before RSS. However, users will notice some differences in files that you've migrated to remote storage. From a command line, users will notice that files residing in remote storage have parentheses around the file size in the directory listing. From Windows Explorer, files appear with a high-latency icon, as the three designated files in Figure 1 show, to denote that they reside in remote storage and will therefore take a bit longer to read or open. These placeholders, known as Reparse Points, tell the Windows I/O subsystem about a migrated file's status.
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