Browse Prior Art Database

Improving Airline Subsystem Performance by Overlapping Semi-synchronous Process

IP.com Disclosure Number: IPCOM000121986D
Original Publication Date: 1991-Oct-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 3 page(s) / 144K

Publishing Venue

IBM

Related People

Johnson, PJ: AUTHOR [+5]

Abstract

DASD Control Units developed for the airline industry have been in existence since 1981. The 3350 was the first product released. The next airlines Control Unit was a 3880 shipped in 1984 containing Automatic Data Transfer (ADT) hardware. Still in use by some airlines today is a 3880 caching Control Unit released in 1985. Released in 1989 is a 3990 caching Control Unit that supports the airline industry requirements.

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This is the abbreviated version, containing approximately 42% of the total text.

Improving Airline Subsystem Performance by Overlapping Semi-synchronous
Process

      DASD Control Units developed for the airline industry
have been in existence since 1981.  The 3350 was the first product
released.  The next airlines Control Unit was a 3880 shipped in 1984
containing Automatic Data Transfer (ADT) hardware.  Still in use by
some airlines today is a 3880 caching Control Unit released in 1985.
Released in 1989 is a 3990 caching Control Unit that supports the
airline industry requirements.

      Common to these products is the airline's software, TPF
(Transaction Process Facility) and the ELLF (Extended Limited Lock
Function) RPQ.
       .  TPF
      TPF supports Record Mode caching.  This allows the user to
select either Record Caching or default to Track Caching.  When
Record Caching is specified only the individual desired DASD record
(i.e., data field) is transferred to/from cache, not a full or
partial track as would be the case when Track Caching.
      When Record Mode Caching is specified all data transfers
between the cache and device occur semi-synchronously.  This means
data can be transferred from/to the device to/from the cache, while
simultaneously different data can be transferred from/to the cache
to/from the host.
      The majority of data transfers between the device and cache
(over 90%) use Record Mode Caching.
      .  ELLF
      ELLF is required to support the airline's software, TPF.  It
allows more than one user to share common resources in a multiple
host configuration.  When used with the first three Control Unit
products (the 3350 and the 3880s), a Hardware Static Switch RPQ
attached to the DASD's A-box is required.  This is needed because
ELLF requires a single path to a device.
      The new DASD devices, 3380 models J and K do not support the
Hardware Static Switch RPQ.  Nor can the 3990 microcode support it
because of the concept of Global Status Devices.  (This means that
all Storage Paths in a subsystem must have access to all attached
devices because the microcode supports status tracks.) Since airlines
still require a single path to a device a "Microcode Static Switch
Function" (MSS) has been implemented in the 3990.
      The MSS causes the host to address a device through a single
Storage Path in the Control Unit.  But unlike the Hardware Static
Switch, all SPs in the Control Unit can access the device.
      When using the 3880 Control Units which require a Hardware
Static Switch on the DASD, "Set Sector Ready" interrupts from the
device can only be detected by the Storage Director which received
the Start I/O.  If the SD is busy when the interrupt is presented, a
"Set Sector Ready Miss" occurs.  (A "Set Sector Ready Interrupt" is a
signal from the device that means it is at the desired position to
begin a data transfer.)
      When using the 3990 with the Microcode Static Switch, "Set
Sector Ready" interrupts from...