Oracle ASM Rebalance and EMC Virtual Provisioning Rebalance Strategies

Oracle ASM performs rebalancing at host level by moving ASM extents across a new set of devices whenever the number of available ASM devices (members) changes.  An ASM rebalancing operation considers device capacity and uses the initialization parameter of rebalance power to determine how many processed participate when performing such an operation.  The operation is performing nondisruptively. An ASM rebalance is base on capacity considerations alone and it does not take in account the frequency of access to data or IO performance. Hence ASM rebalancing helps with spreading data evenly across available devices in single ASM disk group.

EMC Virtual Provisioning automated pool rebalancing on the other hand works at Symmetrix level. By adding data devices to the thin pool and balancing the pool, data device extents can be spread across a larger number of physical disk spindles, which drives higher disk performance without having to change anything by the host or ASM.  If additional capacity is required by the application, new thin devices can be created and added to the application.

Thus ASM rebalance and EMC Virtual Provisioning pool balancing are complementary – ASM allows host-level load balancing and EMC Virtual Provisioning pool balancing allows storage-level load balancing for database IO.