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Chapter 1: Introduction to disaster reco... > Use of the disaster recovery tiers i... - Pg. 9

Operation 1 and 2 Operation 1 If the copy of data contains any of these combinations, then the data is inconsistent (the order of dependent writes was not preserved): Operation 2 and 3 Operation 1 and 3 Operation 2 Operation 3 In the consistency group operation, data consistency means that this sequence is always kept in the backup data. And, the order of non-dependent writes does not necessarily need to be preserved. For example, consider the following two sequences: 1. 2. 3. 4. Deposit paycheck in checking account A. Withdraw cash from checking account A. Deposit paycheck in checking account B. Withdraw cash from checking account B. For the data to be consistent, the deposit of the paycheck must be applied before the withdrawal of cash for each of the checking accounts. However, it does not matter whether the deposit to checking account A or checking account B occurred first, as long as the associated withdrawals are in the correct order. So, the data copy would be consistent if the following sequence occurred at the copy: 1. 2. 3. 4. Deposit paycheck in checking account B. Deposit paycheck in checking account A. Withdraw cash from checking account B. WIthdraw cash from checking account A. In other words, the order of updates is not the same as it was for the source data, but the order of dependent writes is still preserved. Additional detail about Consistency Groups and how they work can be found in The IBM TotalStorage DS8000 Series: Concepts and Architecture, SG24-6452. 1.6 Use of the disaster recovery tiers in this book Our recovery scenarios cover a combination of the tier levels introduced in 1.2, "A breakdown of the seven tiers" on page 2. For example, Chapter 3, "Scenario 2: Complete recovery to same TCP/IP address" on page 39 demonstrates Tier 6 protection of the SAN File System data and storage combined with a Tier 2 protection of the server infrastructure., including the MDSs and clients. Additional recovery scenarios are possible that might provide fully adequate protection based on the cost and recovery requirements of a business. Tier 2, Tier 3, and Tier 4 protection can be provided for the SAN File System environment using a combination of Tivoli Storage Manager and the SAN File System FlashCopy function. For example, in a Tier 2 recovery scenario where recovery is limited to just the data and not the complete SAN File System configuration, Tivoli Storage Manager alone can be used. A Tivoli Storage Manager client installed on a SAN File System client can access and back up all files in the global namespace visible to that client just as it can with a local file system. When SAN File System data is backed up, Tivoli Storage Manager captures both the data itself and the metadata so that subsequent restores can be made, either back to the SAN File System global namespace, or to a local file system or other storage that the client can access. Chapter 1. Introduction to disaster recovery for IBM TotalStorage SAN File System 9