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With asynchronous replication, the I/O must be committed to and acknowledged by the source system so the data can be transferred to the destination in an independent timeframe. Supported storage resources for native asynchronous block replication are volumes, volume groups, and thin clones.
Note: Volume groups are treated as single entities when they are replicated. For virtual machines or tiered applications spanning multiple volumes, consider using volume groups to tie snapshot and replication schedules to the entire application group of volumes. This practice ensures point-in-time consistency across the volumes replicated to the recovery site.
Remote replication between PowerStore systems uses policy-based protection. Asynchronous replication configuration is defined in replication rules (see Figure 7). Protection policies allow the user to configure remote and local protection using replication, snapshot rules, or both. The policies combine one or more rules to fulfill the protection requirements for a storage resource on PowerStore at the protected site. For a valid configuration, a protection policy must contain at least one protection rule whether it is a local or remote protection rule. Each protection policy can contain up to one replication rule, one backup rule and up to four snapshot rules.
The replication rule defines the parameter for the asynchronous replication on PowerStore and is set up on PowerStore at the protected site. The required information for creating a rule includes the PowerStore system at the recovery site, the RPO, and the alert threshold for the planned replication session. When a protection policy with a replication rule is assigned to a storage resource, the configured RPO in the rule is used to set up the internal event scheduler for recurring replication of the storage resource.
For minimal RPO compliance issues, replication cycles are scheduled at 50% of the RPO value and are based on the hour. For example, a one-hour RPO leads to a replication event every 30 minutes to ensure enough overlapping to meet the target of a one-hour RPO. The scheduled RPO events for this example are at x:00 and x:30 every hour. The events for the RPO are based on the configured time and not on the amount of data which is written on the source storage resource. Asynchronous replications usually have more flexible bandwidth requirements. This ability makes it the most common replication method for organizations that allow an RPO that is greater than zero (some amount of data will be lost when recovering from an asynchronous replication). Another benefit of PowerStore asynchronous replication is that the snapshots are transferred to the destination volume. By default, SRM recovers data from the most recent replicated snapshot. However, all snapshots replicated to the recovery site are available for recovery using PowerStore manager or APIs.
Note: Protection policies applied to a replicated volume carry over from the source to the destination after failover and reprotection workflows are run. Using the previous example, if the Exchange Server recovery plan is run and the volumes are failed over and reprotected, they maintain an hourly snapshot and hourly asynchronous replication to the peer storage array.