Library Efficiency

HPSS Tape Library Efficiency on
Versions 7.5.2 and 7.5.3

HPSS versions 7.5.2 and 7.5.3 include new features that directly improve tape library mount rates across multiple tape library types. Improved tape library efficiency reduces the access latency for data on tape. In these versions, HPSS streamlines the way cartridge move requests are processed to maximize efficiency.

7.5.2 Tape Library Efficiency Improvements

Tape improvements have been made to HPSS version 7.5.2 which significantly raise the mount rate efficiency of tape libraries. SCSI PVR improvements that create this increase in efficiency include:

  • Expediting command processing by minimizing communications with the library before sending each command.
  • Further reducing individual move request overhead by minimizing waits during retries
  • Allowing a single control path to queue up to 16 commands by implementing SCSI command queuing
  • Implementing a move scheduler to interlace tape mounts and tape dismounts so the robot is always holding a tape when moving

These changes to HPSS version 7.5.2 drive HPSS efficiency with IBM TS4500 tape libraries from 78% on version 7.5.1 to 99%. The mount rate on 7.5.1 was 702 mounts per hour; it has risen to 894 mounts per hour on 7.5.2.

HPSS 7.5.2 almost doubles the mount rate efficiency with Spectra Logic Libraries from the efficiency seen on 7.5.1. Mount rate efficiency has grown from 42% to 80% on 7.5.2.* The ability to submit multiple move requests with HPSS 7.5.2 has allowed HPSS to support Spectra Logic library’s capability to efficiently order multiple requests.

The following graph illustrates the increased mount rate performance with HPSS 7.5.2:

7.5.3 Tape Library Efficiency Improvements

HPSS 7.5.3 improves tape library efficiency further. These improvements include the following new features:

  • Detection of Spectra Logic library zones so that both robot arms are kept busy.
  • Detection of Spectra Logic TeraPack boundaries in the robot and grouping moves by TeraPack so that multiple cartridges can be mounted and dismounted with each TeraPack move.

The combination of these features allows HPSS 7.5.3 to drive mount rate performance to the hardware rate.

On version 7.5.3, HPSS efficiency with the IBM TS4500 has been maintained at 99% (from version 7.5.2). With Spectra Logic tape libraries, mount rate efficiency has been improved to 99% from 80% on 7.5.2.*

The following graph illustrates the mount rate performance with HPSS 7.5.3:

Future HPSS Versions

In future versions of HPSS, maintaining high mount rate efficiency is a priority. The HPSS roadmap is full of library performance improvements. The HPSS goal is to sustain 99% library efficiency with both IBM TS4500 and Spectra Logic libraries as improvements arrive.