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Self Checkpointing Feature for Storage Devices

IP.com Disclosure Number: IPCOM000079481D
Original Publication Date: 1973-Jul-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Perry, OR: AUTHOR

Abstract

A storage arrangement and checkpoint and mapping technique are shown which provide a self-checkpointing capability for storage volumes, where information is recorded in "granules" of uniform size. The granules are arranged in pairs and two maps are provided, one called a "current" map and the other a "checkpoint" map. A "1" bit in the current map indicates that current information is in the odd granule and a "0" bit that it is in the even granule. A 1 bit in the checkpoint map indicates that the checkpoint information is similarly in the odd granule and a 0 bit that it is in the even granule.

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Self Checkpointing Feature for Storage Devices

A storage arrangement and checkpoint and mapping technique are shown which provide a self-checkpointing capability for storage volumes, where information is recorded in "granules" of uniform size. The granules are arranged in pairs and two maps are provided, one called a "current" map and the other a "checkpoint" map. A "1" bit in the current map indicates that current information is in the odd granule and a "0" bit that it is in the even granule. A 1 bit in the checkpoint map indicates that the checkpoint information is similarly in the odd granule and a 0 bit that it is in the even granule.

For self-checkpointing storage, one granule of each pair is called odd and the other even. At any instant, a granule may contain: a) Current information.

b) Information that was current at the time of the most recent

checkpoint.

c) Information that satisfies both a) and b).

d) Information that satisfies neither a) nor b).

The classification of information in each granule is indicated by the two maps. Each map contains a bit corresponding to each granule pair. The relationship is illustrated using bit values 1 for odd and 0 for even.

When a granule of information is to be recorded in one granule of a particular granule pair, proceed as follows: a) Set the appropriate current-map bit to the value opposite

from the checkpoint-map bit.

b) If the resulting current-map bit is 0, record the information

in the even granule. If 1, record...