Browse Prior Art Database

Fault Tolerant Storage

IP.com Disclosure Number: IPCOM000101976D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 36K

Publishing Venue

IBM

Related People

McGilvray, BL: AUTHOR [+2]

Abstract

In this design, a storage system is backed up by doing dual writes to two independent storage arrays (a prime array and a backup array) with the operational characteristics of doing read/write from the prime array and write only to the backup array. The backup array being used only when a failure exists in the prime array.

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This is the abbreviated version, containing approximately 87% of the total text.

Fault Tolerant Storage

       In this design, a storage system is backed up by doing
dual writes to two independent storage arrays (a prime array and a
backup array) with the operational characteristics of doing
read/write from the prime array and write only to the backup array.
The backup array being used only when a failure exists in the prime
array.

      In a system environment, processors and I/O processors do dual
stores as well as any transfer from expanded storage to main storage
or other input sources to storage.

      In a system that has an intermediate cache, a fetch is done
from both the prime array and the backup array.  This is done in
order to do a store of partial data to the storage block (block being
64 or 128 bytes, for example).

      The fetch to the backup array is to bring data to the cache for
that storage array, if applicable.  It is not required to bring data
all the way to the central processor (CP), for example, since the
data from the prime array will be used by the processor.  There is
synchronization within the CP for the two fetches to compensate for
the timing difference of the data being in the cache or in the array.
This is caused by the cast out of the data from the cache to the
array.  The castout signal to the CPs can come from either cache
(array).  This will cause an invalidate which will cause a refetch by
the CP.

      Upon an error in the fetch from the prime array, the fetch from
the backup array wil...