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Methodology and Apparatus for Handling Checksums for Independent Auxiliary Storage Pools

IP.com Disclosure Number: IPCOM000021607D
Original Publication Date: 2004-Jan-27
Included in the Prior Art Database: 2004-Jan-27
Document File: 1 page(s) / 40K

Publishing Venue

IBM

Abstract

Provide a solution that allows independent auxiliary storage pools (IASP) checksum data to be retrieved from a page being written without seeing any changes that my occur after the write starts and the page is cloned. This is done via a new memory access mode that allows the real address of the page to be used as the virtual address. Accesses to the write pending page can then be done without seeing any changes made to the cloned page.

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Methodology and Apparatus for Handling Checksums for Independent Auxiliary Storage Pools

During a write to a mirrored independent auxiliary storage pools (IASP) , the page being written is marked write pending until both the write to the local IASP and the remote IASP are complete. This means that any touch to that page via its virtual address will result in the page being cloned. This is what happened when checksum data was being collected on the page. The page had been cloned and modified, so the checksum data collected was not from the page being written, but rather from the cloned page.

     Provide a solution that allows the checksum data to be retrieved from the page being written without seeing any changes that my occur after the page is cloned.

     During a write to an IASP, a new memory access mode is introduced for pages that are write pending. This new mode allows the real address of the page to be used as the virtual address. What this means is that the checksum code can access the page via its real address. That page cannot be modified since it is marked write pending. Any modification will cause a clone of the page to a new real page leaving the original unchanged. After write completion (after both the local and remote writes are complete), accesses to the page are no longer allowed via the new memory access mode.

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