Browse Prior Art Database

Dynamic Storage Path Selection

IP.com Disclosure Number: IPCOM000100389D
Original Publication Date: 1990-Apr-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 70K

Publishing Venue

IBM

Related People

Bunten, J: AUTHOR [+5]

Abstract

The dynamic path selection connects a plurality of channels to two parallel storage paths. Each channel connects to a system adapter that communicates with a switch on each storage path. If the storage path is servicing a channel in a short sequence, the system adapter waits for the switch to unlock. If the storage path is servicing a channel in a long sequence, then the storage path polls the other switch. If both switches are busy, then the system adapter informs the channel that both paths are busy. When the switch becomes unlocked, it polls the system adapter to find any waiting channels. The system adapter makes a decision based on the state of the switches to connect to a storage path that can more quickly service the waiting channel.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Dynamic Storage Path Selection

       The dynamic path selection connects a plurality of
channels to two parallel storage paths.  Each channel connects to a
system adapter that communicates with a switch on each storage path.
If the storage path is servicing a channel in a short sequence, the
system adapter waits for the switch to unlock.  If the storage path
is servicing a channel in a long sequence, then the storage path
polls the other switch. If both switches are busy, then the system
adapter informs the channel that both paths are busy.  When the
switch becomes unlocked, it polls the system adapter to find any
waiting channels.  The system adapter makes a decision based on the
state of the switches to connect to a storage path that can more
quickly service the waiting channel.

      As shown in the figure, one storage cluster contains up to
eight system adapters SA A to H, two storage path 0 and 1, with a
switch 10 and 11 included with a respective storage path.  The system
adapters are independent of each other and can compete with each
other for the same storage path to complete channel activity.  To
arbitrate between the system adapters for attachment to the storage
path, each switch 10 and 11 comprises an 8 by 1 switch.  Half of the
system adapters have an affinity for storage path 0 and the other
half have an affinity for storage path 1.  The SA requests selection
to a storage path and the switch associated with that storage path
settles arbitration.

      The system adapters use the following algorithms to determine
which storage to reque...