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METHOD AND MEANS OF ENSURING DATA INTEGRITY UPON FAILURE OF NVRAM CACHE

IP.com Disclosure Number: IPCOM000013544D
Original Publication Date: 2000-Mar-01
Included in the Prior Art Database: 2003-Jun-18
Document File: 1 page(s) / 36K

Publishing Venue

IBM

Abstract

RAID adapters can be configured to run in write-back mode to increase performance. This means that although the adapter tells the host that it is done writing the data to the hard files, it isn't really. The data still remains in the adapter's cache and will be written to the hard files later. If the cache, however, is volatile and the system loses power before the data is flushed to the drives, data loss occurs. To address this problem, the ServRAID II adapter and later uses an NVRAM cache daughter card, that plugs into the host adapter. Data in cache, but not yet flushed to the physical drives, is mirrored in the NVRAM cache. If a system powers down with dirty data in cache, the data will be reconstructed from the NVRAM cache upon power-up. Additionally, the card is made removable such that if the host adapter dies, the NVRAM card can be removed and placed on the new host adapter, and the data reconstructed as before without any data loss.

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  METHOD AND MEANS OF ENSURING DATA INTEGRITY UPON FAILURE OF NVRAM CACHE

RAID adapters can be configured to run in write-back mode to increase performance. This means that although the adapter tells the host that it is done writing the data to the hard files, it isn't really. The data still remains in the adapter's cache and will be written to the hard files later. If the cache, however, is volatile and the system loses power before the data is flushed to the drives, data loss occurs. To address this problem, the ServRAID II adapter and later uses an NVRAM cache daughter card, that plugs into the host adapter. Data in cache, but not yet flushed to the physical drives, is mirrored in the NVRAM cache. If a system powers down with dirty data in cache, the data will be reconstructed from the NVRAM cache upon power-up. Additionally, the card is made removable such that if the host adapter dies, the NVRAM card can be removed and placed on the new host adapter, and the data reconstructed as before without any data loss.

The problem which presents itself, is that a user could take an NVRAM cache daughter card, that he has previously used on another system that was powered down abnormally, and place it in a new system. In this case, the data that's in the daughter card has nothing to do with the new system. If we reconstruct it, we will corrupt the hard file data on the new system.

So...sometimes we want to reconstruct data...sometimes we don't. This disclosure discusses t...