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Method for Master Selection Control Path Optimization

IP.com Disclosure Number: IPCOM000125959D
Original Publication Date: 2005-Jun-24
Included in the Prior Art Database: 2005-Jun-24
Document File: 3 page(s) / 58K

Publishing Venue

IBM

Abstract

This article describes the method for selecting an Asynchronous Continuous Copy Master, and how the control paths for that session are selected or created.

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Method for Master Selection Control Path Optimization

Asynchronous Continuous Copy consists of an environment where an Enterprise Storage System (ESS) acts as a Master for an Asynchronous Continuous Copy. The Asynchronous Continuous Copy consists of three volumes. Volume A is the Asynchronous PPRC source volume. Volume B is the Asynchronous PPRC target volume and Continuous FlashCopy source volume. Finally, volume C is the Continuous FlashCopy target volume. There can be multiple A, B, and C volumes. Volume A is on a different physical box than Volume B and C. An A volume which is selected to be the master volume must have control paths to the subordinate A volumes. These control paths can either be preallocated by the user, or allocated by Replication Manager. If some control paths are preallocated, and some are missing, Replication Manager will establish those missing control paths.

In such an environment preexisting ESS units may already be in use or partially setup to take advantage of this function. A methodology needs to be used which will determine which ESS is in the best position to become the master. Also, any preexisting paths that are available need to be taken into account and used when available. Any missing control paths need to be allocated when needed. An efficient algorithm to manage this environment is needed. The steps involved in that algorithm are documented below:

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    Step (1) in determining which A Volume will be the master, is to query all the paths for each of the A Volumes. The path information is checked to see if any A Volume has a preexisting path to all of the other A Volumes. If an A Volume has connectivity to all the other A Volumes, it is selected as the master and it's preexisting paths are used as the control paths. As we loop through each of these A Volume boxes, we keep track of what paths exist and which paths are missing in order for this A Volume box to be master. If none of the A boxes have all of the necessary control paths, the A Volume box with the least number of missing control paths is selected as the master candidate.

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    An attempt is made to establish the missing control paths. The source LSS has a limi...