Oracle ASM Lesson 6 : Oracle ASM Rebalance

Last updated on July 29th, 2016 at 07:12 am

Oracle ASM rebalance:
 Any change in the storage configuration will trigger a rebalance like disk addition or dropping The main objective of the rebalanceoperation is to always provide an even distribution of file extents and space usage across all disks in thediskgroup. Rebalancing is performed on all database files on a per file basisThe Oracle background process, RBAL, from the ASM instance manages this rebalance.

Process flow for ASM rebalancing:
1. On the ASM instance, a disk is added or dropped from a  diskgroup.
2. This invokes the RBAL process to create the rebalance plan and then begin coordination of the
3. RBAL will calculate estimation time and work required to perform the task and then message the
ARBx processes to actually handle the request. The number of ARBx processes invoked is
directly determined by the asm_power_limit.
4. The Continuing Operations Directory (metadata) will be updated to reflect a rebalance activity.
5. Each extent to be relocated is assigned to an ARBx process.
6. ARBx performs rebalance on these extents. Each extent is locked, relocated, and unlocked. This
is shown as Operation REBAL in V$ASM_OPERATION

The time of rebalance depends on the init.ora parameter asm_power_limit.The range of values for asm_power_limit are 0 to 11; where a value of 11 is full throttle and a value of 1 is low speed. A value of 0, which turns off automatic rebalance, should be used with cautionIt is recommended that  If removing or adding several disks,  it is best to add or remove drives all at once, this will reduce the number rebalance operations that are needed for storage changesQueriesSelect * from v$asm_operation

All the Oracle ASM related articles

ASM: Lesson 1: Introduction

ASM : Lesson -2 ASM disks

Oracle ASM : Lesson 3 ASM Diskgroups

Oracle ASM : Lesson 4 Failure Groups and CSS

Oracle ASM Lesson 5 : ASM Parameters

Oracle ASM Lesson 6 : ASM Rebalance

Oracle ASM Lesson 7:ASM Metadata

Oracle ASM Lesson 8: How to move database to ASM storage

Oracle ASM Lesson 9: ASM queries

How to collect Oracle ASM metadata

Top Oracle ASM queries you should know

Oracle ASM best practice to add disk

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