Avago Technologies Syncro CS 9271-8i - Manual (Page 57)

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Syncro CS 9271-8i Solution User Guide
October 2013 Chapter 4: System Administration
Understanding Failover Operations
4.2 Understanding Failover Operations
A failover operation in HA-DAS is the process by which VD management transitions from one server node to the peer
server node. A failover operation might result from a user-initiated, planned action to move an application to a
different controller node so that maintenance activities can be performed, or the failover might be unintended and
unplanned, resulting from hardware component failure that blocks access to the storage devices.
Figure 38 and
Figure 39 show an example of a failover operation of various drive groups and VDs from Server A to Server B. The
following figure shows the condition of the two server nodes before the failover.
Figure 38 Before Failover from Server A to Server B
Before failover, the cluster status is as follows in terms of managing the drive group and VDs:
 All VDs in A-DG0 (Server A - Drive Group 0) are managed by Server A.
 VD3 in B-DG0 (Server B – Drive Group 0) is managed by Server B.
 The CacheCade VD (CC-VD) in A-CC is managed by Server A and services VDs in drive group A-DG0.
Before failover, the operating system perspective is as follows:
 The operating system on Server A only sees VDs with shared host access and exclusive host access to Server A.
 The operating system on Server B only sees VDs with shared host access and exclusive host access to Server B.
Before failover, the operating system perspective of I/O transactions is as follows:
 Server A is handling I/O transactions that rely on A-DG0:VD1 and A-DG0:VD2.
 Server B is handling I/O transactions that rely on A-DG0:VD0 and B-DG0:VD3.