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Bi-Directional Pulse Detection/Re-Drive in Disk Array

IP.com Disclosure Number: IPCOM000116737D
Original Publication Date: 1995-Oct-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 129K

Publishing Venue

IBM

Related People

Jani, H: AUTHOR [+3]

Abstract

Disclosed is a technique for handling the sourcing of a synchronisation signal in a Redundant Array of Independent Disk (RAID) fault tolerant subsystems. In such systems the use of disk drive spindle synchronisation is required for performance purposes. Arrays of disks are connected by a common spindle synchronisation signal to which each one synchronises the disk rotation to an index pulse generated by one of the disk drives in the array. Usually, a relatively small number of disk drives clustered in close proximity, are connected together by direct wire coupling. The signal driving power of the index disk drive may be insufficient for this purpose.

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Bi-Directional Pulse Detection/Re-Drive in Disk Array

      Disclosed is a technique for handling the sourcing of a
synchronisation signal in a Redundant Array of Independent Disk
(RAID) fault tolerant subsystems.  In such systems the use of disk
drive spindle synchronisation is required for performance purposes.
Arrays of disks are connected by a common spindle synchronisation
signal to which each one synchronises the disk rotation to an index
pulse generated by one of the disk drives in the array.  Usually, a
relatively small number of disk drives clustered in close proximity,
are connected together by direct wire coupling.  The signal driving
power of the index disk drive may be insufficient for this purpose.

      In one array configuration, up to sixteen disk drives may be
split across three individual SCSI buses.  Two of these units may be
configured together, with the disk drives spread across the six SCSI
buses.  For spindle synchronisation, each array is up to six or
twelve disk drives wide split between two units.  This arrangement
poses a number of problems if there is a critical limit on the number
of discrete signals available to provide the synchronisation within
arrays which limits the arrangement to just one signal commoned
between the arrays in the system.  In addition, there is a problem if
the signal driver from the disk drive is only capable of driving up
to sixteen disk drives for synchronization.  The present
configuration has up to thirty-two disk drives hence there is a need
to re-drive the signal.  Furthermore, the separation of the two units
requires an external cable interconnect adding to the load on the
signal.  There is, therefore, a need to drive and receive across this
cable.  Finally, the source of the signal is not known, it could be
in either unit as there is no obvious differentiation between the
two.

      The proposed solution is to connect the two units as follows.
As is shown in Fig. 1, a single spindle synchronization signal is
routed through each system unit and linked by a single card within
the unit.  A connector on this card makes the signal available for
unit to unit connection.  A receiver/driver circuit on the link cards
solves the load problem.

      If the position of the sourcing disk drive is known, then one
simple solution is to have a switch on the link card that sets the
circuit to either drive or receive.  This, however, is dependent on
human intervention and as such is susceptible to errors and as the
result is loss in performance rather than in definitive failure, may
pass undetected.  The present solution involves the driver/receiver
circuit monitoring the inputs to each end of the circuit looking for
incoming pulse signals.  The circuit is enabled only when the
interconnecting cable is plugged into the link card.  The cable
activates the circuit to receive mode on each end, monitoring input
from the units side and from the cable side of the circui...