Re-balancing is a feature wherein when a disk is added or removed from a diskgroup, the content is equally spread across all the available disks (which form the diskgroup). Re-balancing usually takes place after disks have been added or removed. This way disk redundancy is restored once again when a disk failed and a new one had to be added. When more space is required in a diskgroup, disks are added and rebalance takes place as well. This also help increase the throughput as disks are added to the logical diskgroup and content now is balanced and accessed from all across the disks.
Rebalancing a disk group moves data between disks to ensure that every file is evenly spread across all of the disks in a disk group.
When all of the files are evenly dispersed, all of the disks are evenly filled to the same percentage; this ensures load balancing.
The below are the benefits of load balancing:here
* It will decrease the I/O contention on the disk.(Because the data is equally spread to all the disks..).Without Rebalacing concept one disk may have high I/O and one disk may have less I/O
*It will improve the performance.(No need to scan entire file because file is evenly spread across all of the disks in a disk group).
ASM Rebalancing >>>>>>>>>>>>>>>>>>>>>>>
"Rebalancing" is the process of moving file extents onto or off of disks for the purpose of evenly distributing the I/O load of the diskgroup
It occurs asynchronously in the background and can be monitored
In a clustered environment, rebalancing for a disk group is done within a single ASM instance only and cannot be distributed across multiple cluster node to speed it up
ASM will automatically rebalance data on disks when disks are added or removed
The speed and effort placed on rebalancing can be controlled via a POWER LIMIT setting
POWER LIMIT controls the number of background processes involved in the rebalancing effort and is limited to 11. Level 0 means no rebalancing will occur
I/O performance is impacted during rebalancing, but the amount of impact varies on which disks are being rebalanced and how much they are part of the I/O workload. The default power limit was chosen so as not to impact application performance