Factors that Affect RTO

Lists the factors that affect the Recovery Time Objective (RTO).

During a disaster, an administrator must first determine that the link between the primary data center and the secondary data center has failed. Next, the administrator begins the process of switching applications that were running on the primary data center over to the secondary data center. For write applications, the administrator begins converting mirror volumes to read-write volumes, starting with volumes that contain the most critical data. Note that read applications can run on read-only mirrors, but write applications can only run on read-write volumes.

To gauge how long it will take to switch applications from the primary data center to the secondary data center (and to set the RTO accordingly), consider these factors:

  • Detection time (how long it takes to determine that the link is down between the two data centers)
  • Switching time (how long it takes to switch applications from one data center to the other)
  • Promotion time (how long it takes to change read-only mirror volumes to read-write volumes that can run write applications). Promotion time is based on the number of containers in a volume or across volumes.
  • Whether mirror throttling is enabled (the default) or disabled (which speeds up the mirroring process)

Various factors affect the amount of data that can be recovered through the use of mirror volumes. To specify a realistic recovery point objective in your disaster recovery plan, take the following factors into account:

  • Mirror schedule (how often the mirror is synchronized with its source volume) - Note that the first mirror operation is a full synchronization between source and mirror volumes. Subsequent mirror operations are incremental - only the changes that occurred since the last mirror event need to be copied in order to synchronize the contents between the two volumes.
  • Network link between the source volume and the mirror volume (consider the stability and quality of the link, as well as latency, throughput, and other activities across the link)