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Browse Prior Art Database

Fail-Over Method for Fast-Write SCSI Adapter

IP.com Disclosure Number: IPCOM000104843D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 54K

Publishing Venue

IBM

Related People

Tsao, GY: AUTHOR

Abstract

A method is proposed here to enable a good system to take over a failed system when both systems use the non-volatile storage (NVS) SCSI adapter. The adapters of these two systems and disks share a common SCSI bus, as depicted in the figure.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 63% of the total text.

Fail-Over Method for Fast-Write SCSI Adapter

      A method is proposed here to enable a good system to take over
a failed system when both systems use the non-volatile storage (NVS)
SCSI adapter.  The adapters of these two systems and disks share a
common SCSI bus, as depicted in the figure.

      A fast-write SCSI adapter uses NVS to speed up the service to
disk write requests.  The data of disk writes are stored in NVS first
and pushed to disks later.  When a system crashes, it is possible
that data left in the NVS adapter are not updated to the disk yet.
Thus, it is impossible to obtain the 'state' of failed system by just
reading the contents of a shared or twin-tailed disk alone from
another good system.  Therefore, it is difficult to support fail-over
for a NVS SCSI adapter.

      The proposal is to copy incoming 'write' data of adapter1 to
adapter2 by using SCSI peer-to-peer (also called target mode)
protocols.  The NVS adapter1 will not acknowledge the 'write' request
to the host1 until the data copy operation to adapter2 is
successfully performed.  The backup data in the adapter2 are never
pushed to the disk(s) in normal operation mode, i.e., both systems
are up and running.  To reduce the cost, the backup storage in
adapter2 can use low cost DRAM instead of expensive battery backed up
SRAM.  The amount of backup storage in adapter2 is equal to the
amount of NVS storage in adapter1 to ensure that adapter2's backup
storage can back up the data...