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For mission critical Oracle databases, separate the following database components to different ASM disk groups and matching SGs:
All ASM disk groups should use external redundancy (no ASM failure group mirroring) except for Grid Infrastructure (+GRID), which can use normal redundancy (two mirrors). +GRID should not contain any user data, causing it to remain small. When set to normal redundancy, Oracle creates three quorum files rather than one (such as the case when external redundancy is used). Having three quorum files helps during high database workload activity.
By default, ASM uses an Allocation Unit (AU) size of 1 MB (4 MB starting with release 12.2). It also stripes the data across the whole disk group by using the AU as its stripe-depth. This default ASM striping method is called Coarse Striping and is optimal for OLTP-type applications. The DBA might decide to increase the size of the AU from its default, though there is no clear benefit to doing so (except for reduction ASM metadata).
ASM has an alternative striping method called Fine-Grain Striping. With Fine-Grain Striping, ASM selects eight devices in the disk group (if available), allocates an AU on each, and further stripes (divides) the AU into 128 KB chunks. It then allocates data in a round-robin fashion across the eight devices by filling up the 128 KB chunks. When all eight AUs are full, it repeats the process by selecting another set of eight devices.
Fine-Grain striping is the recommended striping method for Oracle objects with primarily sequential writes. Since sequential writes tend to be large I/Os, breaking them into 128 KB stripes improves latencies improve. PowerMax can handle these stripes more efficiently since its track size is also 128 KB.
For this reason, use ASM Fine-Grain striping for the redo logs. This method is especially useful for batch data loads where the redo log writes can be heavy.
If Oracle Temp files become I/O intensive, Temp files can also benefit from Fine-Grain Striping.
Each ASM disk group has its own set of templates, and each template is divided into multiple Oracle file types with their own attributes. Modifying a template (for example, changing the redo logs template to Fine-Grain) only applies to the ASM disk group in which the template was changed.
In addition, template changes do not affect existing ASM allocations. Template changes only affect new extents. Therefore, if you change the redo logs template in the +REDO ASM disk group, you must re-create the log files afterwards. However, re-creating the logs does not take long and can be performed while the database is running.
To inspect the ASM templates, run the following query from the ASM instance:
SQL> select DG.name Disk_Group, TMP.name Template, TMP.stripe from v$asm_diskgroup DG, v$asm_template TMP where DG.group_number=TMP.group_number order by DG.name;
To change the database redo logs template in the +REDO ASM disk group, run the following query:
SQL> ALTER DISKGROUP REDO ALTER TEMPLATE onlinelog ATTRIBUTES (FINE);
To change the temp files template in the +TEMP ASM disk group, run the following query:
SQL> ALTER DISKGROUP TEMP ALTER TEMPLATE tempfile ATTRIBUTES (FINE);