Dell PowerVault MD3420 - Manual (Page 105)

3. Determine candidates for a remote replicated pair.
4. Create the remote relationship.
Performance Considerations
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.
Enabling The Remote Replication (Legacy) Premium Feature
The first step in creating a remote replication is to make sure that the Remote Replication (legacy)
premium feature is enabled on both storage arrays. Because Remote Replication (legacy) is a premium
feature, you need a feature key file to enable the premium feature. The command for enabling the
feature key file is as follows:
enable storageArray feature file=”filename”
In this command, the file parameter is the complete file path and file name of a valid feature key file.
Enclose the file path and the file name in double quotation marks (“ ”). Valid file names for feature key files
end with a .key extension.
Activating The Remote Replication (Legacy) Premium Feature
Activating the Remote Replication (legacy) premium feature prepares the storage arrays to create and
configure replication relationships. After you activate the premium feature, the secondary ports for each
RAID controller module are reserved and dedicated to remote replication use. In addition, a replication
repository virtual disk is automatically created for each RAID controller module in the storage array. As
part of the activation process, you can decide where the replication repository virtual disks will reside,
free capacity on an existing disk group or in a newly created disk group, and the RAID level for the
replication repository virtual disks.
The free capacity that you select for the replication repository virtual disk must have a total of 256 MB of
capacity available. Two replication repository virtual disks are created on this capacity, one for each RAID
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