Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Error Recovery Scenarios for Dual-Gripper Pickers in Libraries

IP.com Disclosure Number: IPCOM000117897D
Original Publication Date: 1996-Jul-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 8 page(s) / 340K

Publishing Venue

IBM

Related People

Means, RJ: AUTHOR [+2]

Abstract

Many of today's library systems have dual-gripper pickers which allow the autochanger to exchange cartridges at a location in a library. This results in higher pick performance than using individual move commands. In most cases, when one of the two grippers fail, the autochanger reports a hard failure and the library stops operating even though the second gripper may still be usable. And, since there are usually more failure points in a dual-gripper picker than in a single-gripper picker, this can result in a dual-gripper picker being less reliable than a single-gripper picker. What is needed is to maintain the performance benefits of a dual-gripper picker while improving the reliability to be equal to or better than the reliability/availability of a single-gripper picker mechanism.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 16% of the total text.

Error Recovery Scenarios for Dual-Gripper Pickers in Libraries

      Many of today's library systems have dual-gripper pickers which
allow the autochanger to exchange cartridges at a location in a
library.  This results in higher pick performance than using
individual move commands.  In most cases, when one of the two
grippers fail, the autochanger reports a hard failure and the library
stops operating even though the second gripper may still be usable.
And, since there are usually more failure points in a dual-gripper
picker than in a single-gripper picker, this can result in a
dual-gripper picker being less reliable than a single-gripper picker.
What is needed is to maintain the performance benefits of a
dual-gripper picker while improving the reliability to be equal to or
better than the reliability/availability of a single-gripper picker
mechanism.  This can be done with an error recovery strategy for a
dual-gripper picker so that if a failure affects one gripper, the
autochanger can continue to operate using the other gripper by
emulating a single-gripper picker.

      The SCSI EXCHANGE MEDIUM command uses a source, a first
destination, and a second destination.  A cartridge is moved from the
source to the first destination, and the cartridge that was in the
first destination is moved to the second destination.

An EXCHANGE MEDIUM command sequence using a dual gripper picker is as
follows:
  1.  position gripper 1 at the source
  2.  pick cartridge 1 from the source location into gripper 1
  3.  position gripper 2 at the first destination
  4.  pick cartridge 2 into gripper 2
  5.  position gripper 1 at the first destination
  6.  put cartridge 1 into the first destination
  7.  position gripper 2 at the second destination
  8.  put cartridge 2 into the second destination

An EXCHANGE MEDIUM command sequence using a single-gripper picker is
as follows:
  1.  position the gripper at the first destination
  2.  pick cartridge 2 into the gripper
  3.  position the gripper at the second destination
  4.  put cartridge 2 into the second destination
  5.  position the gripper at the source
  6.  pick cartridge 1 into the gripper
  7.  position the gripper at the first destination
  8.  put cartridge 1 into the first destination

      In the single-gripper implementation putting cartridge 1 into
the first destination is the last action taken.  In the dual-gripper
implementation putting cartridge 1 into the first destination happens
earlier in the sequence.  Since the first destination is typically a
drive, the dual-gripper implementation makes the cartridge available
for read/write operations sooner.

      What is needed is an error recovery strategy for a dual-gripper
picker so that if a failure affects one gripper, the autochanger can
continue to operate using the other gripper by emulating a
single-gripper picker.  While emulating a single-gripper picker will
lose the performance benef...