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Tuning the SCSI Laser-Off Command to Optical Disk Usage

IP.com Disclosure Number: IPCOM000104159D
Original Publication Date: 1993-Mar-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 4 page(s) / 112K

Publishing Venue

IBM

Related People

Asthana, P: AUTHOR [+4]

Abstract

Rewritable optical disk drives can have a SCSI command that allows the optical library to specify a timeout period for turning the laser(s) off in a drive that is inactive, while leaving the disk spinning. This preserves laser life by curtailing laser power-on-hours (POH) during long periods of device inactivity.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 45% of the total text.

Tuning the SCSI Laser-Off Command to Optical Disk Usage

      Rewritable optical disk drives can have a SCSI command that
allows the optical library to specify a timeout period for turning
the laser(s) off in a drive that is inactive, while leaving the disk
spinning.  This preserves laser life by curtailing laser
power-on-hours (POH) during long periods of device inactivity.

      The current methodology for implementing this SCSI laser-off
command is to use one timeout parameter for all volumes in the
optical library box.  Analysis of customer usage indicates that at
the subsystem level, usage may approach a negative exponential
distribution.  However, on an individual volume level, usage is not
random.  Hence, one blanket timeout parameter is not an optimal
implementation.

      An optical volume is one side of an optical disk when the
optical drive has only one laser transducer and is capable of I/O
operations to only one side of that optical disk at a time.  If the
optical drive has a laser transducer on each side of a mounted
optical disk and can execute I/O operations to both sides of the
mounted disk, then both sides of that optical disk constitute one
volume.

      To take into account the usage pattern of individual volumes,
it is proposed that the laser-off timeout parameter be set equal to
the hit ratio (HR) of that volume in minutes.  This hit ratio is
defined to be the number of read or write operations per mount of
that optical volume.

      Timeout Parameter = HR * 60 seconds/minute
(1)

      A high hit ratio volume, say HR = 6, would have a timeout
parameter of 6 minutes.  A low hit ratio volume, say HR = 1, would
have a much smaller timeout parameter of only 1 minute.  Thus, the
laser(s) would remain on longer for the more active volume, as
denoted by the higher hit ratio, in anticipation of additional
"hits."  The less active volume, denoted by the lower hit ratio, has
a lower probability of additional accesses and can have the laser(s)
turned-off sooner with less risk of having to recalibrate the
laser(s) to the mounted volume.

      If an error is made and the laser is prematurely turned off,
there may be a short recalibration time involved.  It is proposed
that the write activity not be recalibrated if only a read activity
is requested.  This may save time in recalibration.

      This tuning of individual volumes, based on their individual
hit ratios, tailors the amount of laser inactivity (before being
turned off) to the volume mounted at that time in the device.  This
makes the optical library far more versatile.

      Further versatility can be obtained by providing a limited
amount of adaptability to the timeout parameter.  If the laser-off
command was premature and a subsequent access was issued to that
mounted volume, the timeout parameter for that mounted volume could
be reset to twice the hit ratio (again in minutes).  Thus, the
probability of subsequent p...