The HPSS component that manages tape mounts for modern tape libraries is the HPSS SCSI PVR. HPSS now streamlines the way cartridge move requests are processed. Delivering features that improved the efficiency of tape mounts allows HPSS to: maximize tape library mount rate (higher mounts per hour); and minimize access latency to data on tape (shorter time to first byte).
Library Efficiency
Maximizing Tape Library Mount Rate Performance
HPSS SCSI PVR Improvements #1
The following features significantly raise the mount rate performance for all modern tape libraries that use the HPSS SCSI PVR:
- 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.
The mount rate performance of the IBM TS4500 tape library climbed from 78% to 99% of the manufacturer’s mounts per hour. Before the software updates, HPSS performed 702 mounts per hour. After the updates, HPSS performed 894 mounts per hour. The mount rate performance of the Spectra Logic tape library climbed from 42% to 80% of the manufacturer’s mount per hour exchange rate. Because we were unable to reach 99% of the manufacturer’s mount per hour exchange rate for the Spectra Logic tape library, subsequent improvements were needed (see HPSS SCSI PVR Improvements #2 below).
HPSS SCSI PVR Improvements #2
The next set of HPSS SCSI PVR improvements were specifically implemented for Spectra Logic tape libraries. The HPSS developers worked closely with the Spectra Logic team to implement features to maximize tape handling efficiencies. The following changes were implemented for the Spectra Logic tape libraries:
- 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.
Before the software updates, HPSS reached 80% of the manufacturer’s mounts per hour. After the updates, HPSS reached 99% of the manufacturer’s mounts per hour.
Future HPSS Versions
In future versions of HPSS, maintaining high mount rate efficiency is a priority. The HPSS goal is to sustain 99% library efficiency with all tape libraries.