Dell EqualLogic PS6210XS EqualLogic Group Manager Administrator s Guide PS Ser - Page 237

Eventually, the oldest replicas are deleted from the replica set to free space for new replicas. The amount of space that you allocate for storing replicas limits the number of replicas you can keep on the secondary group. NOTE: To ensure that a complete copy of volume data exists on the secondary group, the most recent, complete replica of a volume cannot be deleted. To access or recover volume data from replicas, you can: • Clone an individual replica to create a new volume on the secondary group. • Promote the replica set to a recovery volume (and snapshots) on the secondary group and configure initiators to connect to the recovery volume. If the primary group becomes available, you can replicate the recovery volume to the primary group and then fail back to the primary group, returning to the original configuration. NOTE: Replication is used primarily for disaster recovery and does not take the place of a comprehensive backup strategy. You can manually delete replicas and replica sets that are no longer needed. You cannot delete the most recent, complete replica from a replica set, but you can delete the entire replica set, which disables replication on the volume. NOTE: For information about NAS replication options, refer to NAS Volume Replication Operations. Replication Types PS Series firmware provides the following methods for automatically replicating block volumes to provide protection against accidental data loss: • Traditional replication (often referred to as Replication or Auto-Replication) is a point-in-time process that is conducted between two groups, often in geographically diverse locations. Replication provides protection against a regional disaster such as an earthquake or hurricane. • Synchronous replication (also known as SyncRep) is a real-time process that simultaneously writes volume data across two different pools within the same PS Series group. This method is useful for maintaining two copies of a volume's data in the same data center, or dispersed to two different facilities on the same campus or in the same metropolitan area. NOTE: You cannot enable synchronous replication on a volume for which traditional replication is configured, and you cannot enable traditional replication on a volume for which synchronous replication is configured. In addition to these two replication methods, the Dell Fluid File System (FluidFS) release available on FS7500 and FS76x0 series NAS appliances allows you to replicate NAS containers between EqualLogic NAS clusters. This point-in-time NAS replication uses spaceefficient snapshots of NAS containers to replicate file data. You can manage both block and NAS replication using the Group Manager interface. NOTE: Throughout the firmware documentation, generic references to replication always refer to traditional replication. A third type of replication, called manual transfer replication, accommodates less common instances where the network link between groups might be insufficient to support large data transfers. This method is typically done as a precursor to enacting traditional replication, so the initial full-volume transfers do not have to be done over the network. Manual transfer replication involves copying the data to external media, then physically transferring it and recopying it to the other member. See the Dell EqualLogic Manual Transfer Utility Installation and User's Guide for more information. Plan Your Volume Replication Environment To help ensure successful replication, for each volume that you want to replicate follow these steps to set up your replication environment: 1. Gather the following information to help you determine how much replication space you need: • Number of replicas you want to keep • Average time span between each consecutive replica About Backing Up and Protecting Your Data 237