Thursday Sep 15, 2011

How Content Management Makes Tape Drives More Efficient

Guest blog by Steve Aaker and Jamie Giovanetto

Oracle StorageTek's Enterprise Library Software (ELS) is the storage management software available for these Oracle StorageTek Tape Storage mainframe products:

In addition to its hardware enablement functions, ELS provides a rules-based content manager that can significantly increase the efficiency of your tape drives and systems. It's called the Library Content Manager or LCM for short, and it is described in the documentation for the ELS software.

For physical tapes, which can be native data or scratch cartridges, Multiple Volume Cartridges (MVCs), or cleaning cartridges and empty (free) storage cells, LCM places the tapes in the best location to:

  • Maximize the efficiency of the enabling software selections
  • Minimize the robotics activity at job mount time.

In the virtual tape environment, LCM controls whether a volume is in Oracle's StorageTek Virtual Storage Manager System buffer or only on an MVC at the appropriate time.

This content management capability can dramatically increase the efficiency of your tape storage.

An Example

Let's take the case where a StorageTek SL8500 modular library system from Oracle is totally full of cartridges and has no content management. All mounts and dismounts for the tapes in the library occur when required, but the question is whether that is sufficient. It is the minimum expected action, to be sure, but is it being accomplished in an efficient manner? If the cartridge to be mounted is in Library Storage Module (LSM) 03 and the drive where it is to be mounted is in LSM 00 (because that is the only location for that type of drive), the mount will take five major robotics actions. At dismount time, because there are no free cells, it will take another five major robotics actions to return the cartridge back to its source cell. In both directions, at least one of these robotic actions will be a move through the entire length of the library. When complete, the cartridge is back in LSM 03 and the drives it can be mounted on are still in LSM 00. Each time the volume is mounted, this scenario is repeated.

Now, let's look at what the same mount would look like in a content-managed StorageTek SL8500 modular library system. First, the cartridge to be mounted would have been placed in LSM 00 by a prior management run, which would have placed it in the LSM where the drives on which it could be mounted are located. Because of this management activity, the mount would require only two robotics actions, and the dismount would require the same. The reduction of three robotics actions, including that move through the entire length of the library, significantly reduces overall robotics time and results in much faster mount time. The cumulative mount times directly affect overall production time, so proper placement of volumes has a significant impact on production performance.

However, you might ask, "Didn't the cartridge have to be moved to the right place at some time? Didn't that take robotics activity?" Of course, it did. The difference is that content management activity would have been done outside the production job's execution time. In addition, the cartridge would have been placed where it can be mounted many times without requiring the many robotics actions required in the unmanaged example.

Note that this is just one of many examples where significant performance improvements can be obtained by active, rules-based content management. At its fullest implementation level, StorageTek LCM can bring scheduled production mounts down to sub-second levels in the virtual environment and, in some cases, to an average mount time that is approximately half the average mount time for an Oracle StorageTek SL8500 modular library system in the physical environment. Combined with its other capabilities and the underlying hardware and enabling software environment, Oracle's StorageTek Library Content Manager offers great enhancements to the automated tape environment.

- Steve Aaker and Jamie Giovanetto


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