Sun Microsystems StorageTek 6140 Administration Manual page 100

The software replicates data from a primary volume to a secondary volume. The
association between the primary and secondary volumes constitutes a replication
set. After the volumes in a replication set have been initially synchronized, the
software ensures that the primary and secondary volumes contain the same data on
an ongoing basis.
Note: There are exceptions if you use asynchronous replication mode. See "About
Replication Modes" on page 91 for more information.
Note: Third-party applications can continue to write to the primary volume while it
is replicating, but the secondary volume is read only.
The software transports data between the two arrays by means of synchronous or
asynchronous replication mode, using a dedicated Fibre Channel (FC) connection
(FC port 4 for the 6140 array, and host port 2 for the 6130 array). Both of the arrays
with volumes participating in the replication set must be registered with Sun's
management software, and must be reachable through the out-of-band management
network.
Note: The system does not provide built-in authentication or encryption for data
traveling outside of your data center over a long-distance replication link. It is
assumed that customers implementing data replication strategies using multiple
arrays will replicate data over secure leased lines or use edge devices to provide
encryption and authentication. For assistance with setting up appropriate security,
contact Sun Client Solutions.
If there is a break in the network or if the secondary volume is unavailable, the
software automatically switches to suspended mode, in which it ceases replication
and tracks changes to the primary volume in a separate volume known as a
replication repository. When communication is restored, the software uses the
information in the replication repository volume to resynchronize the volumes and
returns to replicating the data.
When replicating data in synchronous replication mode, the software preserves
write order consistency. That is, the software ensures that write operations to the
secondary volume occur in the same order as the write operations to the primary
volume. This ensures that the data on the secondary volume is consistent with data
on the primary volume and does not compromise an attempt to recover the data if a
disaster occurs at the primary volume.
If you need to ensure write order consistency across multiple volumes, such as for
an application that builds its database on multiple volumes, you can place multiple
replication sets into the consistency group. Each array supports only one consistency
group and replication sets in the consistency group must use asynchronous
replication mode. The consistency group enables you to manage several replication
sets as one. By using the consistency group, the software maintains write ordering
for volumes in a group to ensure that the data on all secondary volumes is a
consistent copy of the corresponding primary volumes.
84 Sun StorageTek Array Administration Guide • May 2006