Optical Storage and Hierarchical Storage Management

Although the adoption rate for Network Attached Storage (NAS) and Storage Area Network (SAN) continues to increase, a majority of today's storage, particularly storage for applications running on Windows servers, is still Direct Attached Storage (DAS). DAS presents many challenges for administrators—particularly in the areas of capacity management and data availability. At most companies, as much as 80 percent of the data on primary disk is inactive (i.e., users haven't accessed the data frequently, if at all, for more than 30 days).

One way that systems administrators solve the management problem that these large amounts of inactive data present is to use long-term archival storage through optical or other inexpensive media. Data archiving combined with Hierarchical Storage Management (HSM) is an excellent solution when you have a low probability of needing to access the archived data.

Because of its reliability and performance, optical technology is appropriate for long-term archival storage. Optical technology includes different secondary storage technologies, including but not limited to erasable optical; write once, read many (WORM); DVD-RAM; CD-R; CD-ROM; CD-RW; magneto-optic (MO); DVD-R; DVD-ROM; and DVD-RW. Differences in recording techniques, capacity, and performance make each technology unique. For example, CD-RW and DVD-RAM drives write to media in a process that uses a laser only, whereas MO uses a laser in conjunction with a magnet. Individual pieces of DVD-R and DVD-RAM media are dual-sided and support capacities of 4.7GB; users can erase and rewrite the data hundreds of thousands of times. In contrast, MO media is highly durable—individual pieces of media can withstand more than a million writes, which makes it more durable than the others. The latest MO technology supports 9.1GB platters and offers an archival life span of more than 30 years.

DVD-RAM, CD-R, CD-RW, and DVD-R disks, towers, and jukeboxes are desktop technologies for small office/home office (SOHO) environments. DVD is excellent media that can help departmental and SOHO users with better storage management, backup, and archiving. Recent DVD-R features (e.g., support for combo drives, incremental write capabilities) continue to ensure that these low-cost technologies have a future in comprehensive storage environments. In particular, CD-R (currently supporting 650MB per platter) will continue to lead the audio market, and DVD will lead the video market. In addition to long-term archival storage, MO is an excellent media for enterprise applications that require frequent reads, such as document-imaging management and Computer Output to Laser Disk (COLD).

But what if users need inactive, archived data to remain immediately available? One solution is "nearline storage," which has several options for delivering nearline availability, including NAS and emerging virtual-tape solutions. For particular applications and markets, however, optical storage is one of the most mature technologies and one of the most cost-effective solutions. The same industries and applications that effectively use optical technologies for archiving purposes (e.g., document-imaging management, COLD, medical-records applications, government-data preservation) might elect to configure optical technologies for nearline access.

To provide data migration for archival or nearline storage purposes with periodic, transparent access, optical-storage technologies in the Windows environment are more cost effective when you combine them with software technologies that permit primary disk expansion on the fly—known collectively as HSM. HSM lets you set policies based on predefined data-access and availability needs, then migrates data to secondary storage (including optical storage) on either a scheduled or event-triggered basis. HSM gives applications transparent, as-needed access to data, usually by leaving a pointer on the magnetic disk to the exact physical location of the migrated data.

After you migrate data to optical storage, you no longer need to back up that data. An HSM solution that migrates data to nearline storage and leaves pointers on the original magnetic disk is particularly useful to administrators who want to reduce backup costs while retaining high availability. The data is available through access to optical media; however, because the data doesn't reside on the primary disk, a full backup doesn't include stagnant data. This combination of HSM and optical media provides significantly reduced backup and recovery windows.

Optical technologies' share of the storage-medium market might be decreasing. However, the technology will continue to add value in certain storage configurations and for particular applications for the foreseeable future, especially when paired with storage-management tools such as HSM.

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