The synchronization services component (CSS) of the Oracle Clusterware maintains two heartbeat mechanisms
1.) the disk heartbeat to the voting device and
2.) the network heartbeat across the interconnect--which establish and confirm valid node membership in the cluster.
Both of these heartbeat mechanisms have an associated timeout value.
The disk heartbeat has an internal i/o timeout interval (IOT), in seconds,
where an i/o to the voting disk must complete.
The misscount parameter (MC), as stated above, is the maximum time, in seconds, that a network heartbeat can be missed.
The disk heartbeat i/o timeout interval is directly related to the misscount parameter setting.
If I/O latencies to the voting disk are greater than the default IOT calculations , the cluster may experience CSS node evictions depending on
(a)the Oracle Clusterware (CRS) version,
(b)whether merge patch has been applied and
(c)the state of the Cluster.
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