Dell PowerVault MD3260i - Manual (Page 87)

corrected (the secondary virtual disk is placed online or recovered to an Optimal status), then synchronization is
required. The replicated pair then transitions to a Synchronization in Progress status.
Resynchronization
Data replication between the primary virtual disk and the secondary virtual disk in a replication relationship is managed
by the RAID controller modules and is transparent to host machines and applications. When the RAID controller module
owner of the primary virtual disk receives a write request from a host, the RAID controller module first logs information
about the write to a replication repository virtual disk. The RAID controller module then writes the data to the primary
virtual disk. The RAID controller module then initiates a write operation to copy the affected data to the secondary
virtual disk on the remote storage array.
If a link interruption or a virtual disk error prevents communication with the secondary storage array, the RAID controller
module owner of the primary virtual disk transitions the replicated pair into an Unsynchronized status. The RAID
controller module owner then sends an I/O completion to the host sending the write request. The host can continue to
issue write requests to the primary virtual disk, but remote writes to the secondary virtual disk do not take place.
When connectivity is restored between the RAID controller module owner of the primary virtual disk and the RAID
controller module owner of the secondary virtual disk, the virtual disks must be resynchronized by copying the blocks of
data that changed during the interruption to the secondary virtual disk. Only the blocks of data that have changed on the
primary virtual disk during the link interruption are copied to the secondary virtual disk.
CAUTION: Possible loss of data access – Any communication disruptions between the primary storage array and
the secondary storage array while resynchronization is underway could result in a mix of new data and old data on
the secondary virtual disk. This condition would render the data unusable in a disaster recovery situation.
Remote Replication Group
After your Remote Replication premium feature is activated on both local and remote storage arrays, you must create
Remote Replication groups on the local storage array.
A replication group contains at least one replicated virtual disk pair, one on the local storage and one on the remote
storage array, that share data synchronization settings. Multiple replicated pairs can reside in a replication group, but
each pair can only be a member of one Remote Replication group.
The following attributes also apply to a Remote Replication group:
• The local storage array serves as the primary side of the Remote Replication group, while the remote storage
array serves as the secondary side of the Remote Replication group.
• At the virtual disk level, all virtual disks added to the Remote Replication group on the local storage array serve
as the primary role in the Remote Replication configuration. Virtual disks added to the group on the remote
storage array serve the secondary role.
Once you have selected virtual disks at both the remote and local storage array that you want to pair in a replication
relationship, adding them to a replication group actually begins the replication synchronization process.
For more detailed information on the role of Remote Replication groups, see the
Administrator's Guide .
Previous Users Of Remote Replication (Legacy) Premium Feature
If you have upgraded (or plan to upgrade) your RAID controller firmware version to a level that supports both legacy and
non-legacy Remote Replication, any legacy replication configurations you have previously set up will be unaffected, and
will continue to function normally.
87