94 Using the Remote Replication Premium Feature
How Remote Replication Works
When you create a remote replicated pair, the remote replicated pair consists
of a primary virtual disk on a local storage array and a secondary virtual disk
on a storage array at another site. A standard virtual disk might only be
included in one replicated virtual disk pair.
The primary virtual disk is the virtual disk that accepts host I/O activity and
stores application data. When the replication relationship is first created, data
from the primary virtual disk is copied in its entirety to the secondary virtual
disk. This process is known as a full synchronization and is directed by the
RAID controller module owner of the primary virtual disk. During a full
synchronization, the primary virtual disk remains fully accessible for all
normal I/O operations.
The RAID controller module owner of the primary virtual disk initiates
remote writes to the secondary virtual disk to keep the data on the two virtual
The secondary virtual disk maintains a replication (or copy) of the data on its
associated primary virtual disk. The RAID controller module owner of the
secondary virtual disk receives remote writes from the RAID controller
module owner of the primary virtual disk but will not accept host write
requests. Hosts are able to read from the secondary virtual disk, which appears
In the event of a disaster or a catastrophic failure at the primary site, you can
perform a role reversal to promote the secondary virtual disk to a primary role.
Hosts then are able to read from and write to the newly promoted virtual disk,
and business operations can continue.
Replication Repository Virtual Disks
A replication repository virtual disk is a special virtual disk in the storage array
that is created as a resource for the RAID controller module owner of the
primary virtual disk in a remote replicated pair. The RAID controller module
stores replication information on this virtual disk, including information
about remote writes that are not yet complete. The RAID controller module
can use this information to recover from RAID controller module resets and
the accidental powering down of the storage arrays.
book.book Page 94 Wednesday, June 8, 2011 12:20 PM