Overview
When developing EVM-database application jobs, you can optimize performance by considering:
Storage unit replication methods
Configuration of source units in the StorageWorks subsystem
StorageWorks subsystem utilization and unused disk capacity
These considerations interact with each other and influence your decisions on how to best configure storage units.
Replication Methods
Replication methods that are available in an EVM job are clone and snapshot. Each EVM job that you design will support one replication method. You cannot mix replication methods within a single job.
Snapshot Replication Method
The snapshot method produces a nearly instantaneous virtual copy of a storage unit. Because of its speed and minimal impact on database operations, it is an excellent choice for many types of EVM jobs.
When the EVM job is actually run, unused disk capacity on StorageWorks subsystem must equal or exceed the disk capacity of the source units being replicated. Because the snapshot method stores part of the replicated unit in the controller cache this method is not recommended when the resulting BCV unit is to be retained for extended use.
Clone Replication Method
The clone method produces a duplicate unit that resides entirely on disk. It is a good choice for jobs where the resulting BCV unit will be retained for extended use. Unit replication speed depends upon the configuration of the StorageWorks source unit and the utilization of the storage array. With planning, the clone method provides near instantaneous replication during an EVM job.
Three-member Clone Approach. To achieve near instantaneous replication, each source unit should be configured in StorageWorks as a three-member mirror set. In this configuration, EVM can instantly split the third member and mount it on the server specified in the EVM job.
Before running the EVM job, you must configure the unit and allow enough time for its members to normalize. See also Quick Clone.
Two-member Clone Approach. In this approach, each source unit is configured in StorageWorks as a two-member mirror set. When the EVM job is actually run, unused disk capacity on the StorageWorks subsystem must equal or exceed the disk capacity of the units being replicated. EVM will automatically add a third member to the mirror set, normalize the members, then split the third member to create the new BCV unit.
Combination Approach. In a single EVM job, you can use the clone method to replicate different types of units, such as two-member mirror sets, three-member mirror sets and JBODs. When creating jobs in which replication speed is a primary concern, you should consider the implications of how each unit is configured in the StorageWorks subsystem.