ASM – Intelligent Data Placement

Oracle Database 11g Release 2 adds intelligent data placement (IDP) support for JBOD (just a bunch of disks) configurations for ASM disk groups. IDP leverages geometry of disks and will place hot files on the outer most edge of the spindles and cold files in the inner rings of the drives. In addition, files that are accessed with similar patterns are placed close to each other to reduce latency.

IDP is supported by both ASM Configuration Assistant (ASMCA) and Enterprise Manager.

The outermost tracks provide greater speed and higher bandwidth. IDP works at disk group attribute level or at the file level and can be modified after the disk group is created. IDP is suited for situations where:
1. Disk groups that are > 25% full
2. Database datafiles are accessed at different rates
3. JBOD configurations – LUNs carved out of SANs are not suited for IDP

You can set IDP for only new files. Existing files must go through a rebalance operation to leverage IDP. In order to leverage IDP, both COMPATIBLE.ASM and COMPATIBLE.RDBMS disk group attributes must be set to a value of 11.2.0 or higher. IDP can be set with the following SQL syntax:

1	1.  ALTER DISKGROUP DATA ADD TEMPLATE
2	2.  ALTER DISKGROUP DATA MODIFY TEMPLATE

 

3	3.  ALTER DISKGROUP DATA MOFIFY FILE

For example:

1	alter diskgroup data add template hotfiles attributes (hot mirrorhot);

IDP information can be retrieved by querying V$ASM_DISK, V$ASM_DISK_IOSTAT, V$ASM_FILE and V$ASM_TEMPLATE views.

Columns from V$ASM_DISK that are of particular interest are:

01	HOT_READS                      NUMBER
02	HOT_WRITES                     NUMBER

 

03	HOT_BYTES_READ                     NUMBER
04	HOT_BYTES_WRITTEN                  NUMBER

 

05	COLD_READS                     NUMBER
06	COLD_WRITES                        NUMBER

 

07	COLD_BYTES_READ                    NUMBER
08	COLD_BYTES_WRITTEN             NUMBER

 

09	HOT_USED_MB                        NUMBER
10	COLD_USED_MB                       NUMBER

New columns in v$asm_template that apply to IDP are:

1	PRIMARY_REGION                     VARCHAR2(4)
2	MIRROR_REGION                  VARCHAR2(4)