MAA - Oracle 10gR2 Redo Transport and Network Best Practices

Maximum Availability Architecture
In this example, the total runtime for this recovery session was 590 seconds. The
statspack report shows the top waits are I/O related:
Data file init write, 120s, I/O wait
log file sequential read, 423s, I/O wait
parallel recovery slave next change, 1645s, idle slave
event
Log file sequential read and data file init write are coordinator I/O waits. 543/590s =
89% of the time coordinator is waiting on I/O. This immediately indicates the
recovery is I/O bound. If this environment had been a synchronous I/O system,
the wait event would be db file parallel read rather than recovery read.
If parallel recovery read buffer free is high and recovery read (async I/O) or db file sequential
read (sync I/O) is high, this would be indicative of the slaves waiting for I/O.
For file systems where asynchronous I/O is not possible, then use Oracle Disk
Manager (ODM), packaged with the release of Veritas Storage Foundation
appropriate for the version of the Oracle Database in use. ODM has been shown
to provide async-like performance. In addition to using ODM you should also set
the database initialization parameters: filesystemio_options='setall'
and _media_recovery_read_batch=[512 or 1024]
Oracle Active Data Guard: Oracle Data Guard 11g Page 33