Dell PowerVault MD 32XX/36XX Series Storage Arrays CLI Guide

Keep these performance considerations in mind when you create replication relationships:

• The RAID controller module owner of a primary virtual disk performs a full synchronization in the background while processing local I/O writes to the primary virtual disk and associated remote writes to the secondary virtual disk. Because the full synchronization diverts RAID controller module processing resources from I/O writes, full synchronization can have a performance impact to the host application.
• To reduce the performance impact, you can set the synchronization priority level to determine how the RAID controller module owner will prioritize the full synchronization relative to other I/O activity. To set the synchronization priority level, consider these guidelines:
  • A full synchronization at the lowest synchronization priority level takes approximately eight times as long as a full synchronization at the highest synchronization priority level.
  • A full synchronization at the low synchronization priority level takes approximately six times as long as a full synchronization at the highest synchronization priority level.
  • A full synchronization at the medium synchronization priority level takes approximately three-and-a-half times as long as a full synchronization at the highest synchronization priority level.
  • A full synchronization at the high synchronization priority level takes approximately twice as long as a full synchronization at the highest synchronization priority level.
• When the replicated virtual disk pair is in a Synchronization in Progress state, all host write data is copied to the remote system. Both RAID controller module I/O bandwidth and I/O latency can affect host write performance. Host read performance is not affected by the replication relationship.
• The time that it takes for data to be copied from the primary virtual disk to the secondary virtual disk might impact overall performance. This impact is primarily caused by the delay and system resource required for copying data to the remote replication. Some delay might also occur because of the limit to the number of simultaneous writes.