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GMIR Consistency Group Formation - Surrender Mechanism Disclosure Number: IPCOM000197247D
Publication Date: 2010-Jun-29
Document File: 2 page(s) / 35K

Publishing Venue

The Prior Art Database


Global Mirror (GMIR) is a consistent extended distance data replication technology. Volumes are grouped into a consistent session and snapshots of the session are taken at desired intervals. This consistent volume data is then drained over to a remote location via Global Copy relationships. Once the consistent data is at the remote site a FlashCopy is taken that will store any changes so that the customer can revert back to a consistent point. Any I/O writes that come in while a snapshot is draining are instead tracked in a separate bitmap. If an I/O write comes in for a track that still needs to be drained as part of a snapshot, then this is called a Global Mirror collision and the track must be immediately copied over. Global Mirror collisions affect host performance as the write will not complete until the track is copied to the remote site. An intelligent solution that utilized data transfer trends and evaluated probability of completion, would help reduce GMIR collisions and improve host performance.

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GMIR Consistency Group Formation - Surrender Mechanism

General Implementation

This is a mechanism that automatically detects when a consistency group formation will be impossible within the given time allotted based on the current IO performance of the given global mirror master, and its predicted future performance. In this case the consistency group formation will be prematurely interrupted and the global mirror master will be put in the monitor state which will attempt to predict when the formation can be done in the future successfully.

This premature interruption of the formation will allow this process to get out of the way of other stress on the machine, thus increasing the likelihood that this other stress will complete successfully and a future time when the consistency group formation can complete will be found. Another advantage is that the IO rates of the volumes that were trying to form consistency groups will be returned to normal faster than before.

One Preferred Implementation

Figure 1. Simplified GMIR Flowchart with invention

1. Query OOS (out of sync) Phase - More tracks to drain

Once in the query OOS phase GMIR will query at a set interval waiting for the OOS tracks to drain down to zero. This phase will now store the number of OOS tracks at each query interval in some OOS history data structure.


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2. Surrender or Drain Timer Expired

GMIR has a drain timer which defines how lon...