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Many IT departments have seen the benefits of implementing an enterprise-class tape library. No longer do administrators or tape librarians have to shuffle throughout the data center looking for and documenting the receipt of backup tapes. In addition, we now have a better idea about the validity of the data on the tapes that are collected for archival.
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Don't waste switch resources by using a port for each tape drive in the library.
Do conserve ports by using arbitrated loop switches to aggregate traffic from the fabric to the drives.
Of course, this is the end result of much planning, bumps, bruises and failed backups. Enterprise-class tape libraries are important to lowering the overall cost of storage management, software and hardware. However, to have any chance of achieving the ROI that you were promised by your vendors, a properly sized library with the correct tape format and library connectivity must be used.
When I am performing interviews with application owners regarding the longevity of their application's data, rarely is there any mention of a corporate-wide data policy, nor is there any solicitation of information from the application's users. Instead, what usually happens is the application owner looks up at the ceiling and spouts out some safe number that doesn't necessarily coincide with the corporation's goals of profitability or liability for that matter.
If you can, have a corporate-wide data retention policy in place and signed by the chief in charge. What's needed here is a thorough risk analysis that combines input from the application users, the people responsible for providing recovery services and the people whose fate depends on the viability of the corporation after data is lost. You may also benefit from an outside vendor to provide industry experience and expertise.
The data retention policy will allow you to achieve some predictability in your tape usage, and as a result, in your tape and tape drive needs. With a referable corporate-wide data retention policy as your shield, you can start notifying departments of the enforced retention policy as soon as a decision has been made for departments to share a tape library.
Of course you'll often find that one person in particular will want to have more influence on the changes taking place. For example, your retention policy might indicate that all developmental databases are backed up completely once a week, and incrementally on every other day. However, the Oracle DBA may feel safer if you did a full backup every day. Resist - as long as you have the retention policy on your side. Take the default stance of deny, but do it nicely.
Even a small change like that can create problems with backup schedules. Pretty soon, you're experiencing other failures because resources (tape drives) that were previously available at 3 a.m. on Tuesday are no longer available because a storage policy was violated, without taking into account the available resources and the needs of other clients backing up at the same time.
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Once the retention policy has been implemented for a few quarters, and depending on the desired schedule of your tape vault vendor, you can determine how large of a tape library you'll need for your solution. Three quarters - including fiscal and calendar year end if possible - worth of trending data under the retention policy should give you some idea about the projected growth that your selected tape library must accommodate.
Tape drive selection
Determine whether your current media choice will provide your applications with the level of service it needs. For example, a backup and recovery solution will not necessarily use the same tape format as a hierarchical storage management (HSM) solution. You may have a couple of servers generating backup traffic to your tape library used for backups, and a couple hundred users generating read requests to the tape library supporting the HSM solution.
In that scenario, the library supporting the backup of a few servers may be best served by using DLT or LTO technologies. However, when those servers' data is migrated from disk to tape as a result of HSM, the larger user community could potentially overrun the HSM tape library because of the slow load times of the selected tape drive technology. Although it isn't desirable to support two tape formats, in some cases it may be necessary, depending on the traffic patterns of the applications involved.
This was first published in October 2002