Oracle Automatic Storage Manager (ASM) enables redundancy and optimal performance out-of-the-box. However, consider the following items as they improve performance and/or increase availability:
Implement multiple access paths to the storage array using two or more HBAs (host bus adaptors) or initiators.
Deploy multipathing software over these multiple HBAs to provide I/O load-balancing and failover capabilities.
Use diskgroups with disks of similar size and performance. A diskgroup containing a large number of disks provides a wide distribution of data extents, thus allowing greater concurrency for I/O and reducing the occurrences of hotspots. Because a large diskgroup can easily sustain various I/O characteristics and workloads, a single (database area) diskgroup can be used to house database files, log files, and control files.
Use diskgroups with four or more disks, and make sure these disks span several backend disk adapters.
Oracle generally recommends no more than two diskgroups. For example, a common deployment can include four or more disks in a database diskgroup (DATA diskgroup, for example) spanning all backend disk adapters/directors and eight to ten disks for the fast recovery area diskgroup. The size of the fast recovery area depends on what is stored and how much—full database backups, incremental backups, flashback database logs, and archive logs. An active copy of the control file and one member of each of the redo log groups are stored in the fast recovery area.
See Oracle’s High Availability Architecture and Best Practices Manual for more details on these topics.