HP XP Racks - Manual (Page 9)

Volume pairs
As described previously, original data is stored in the P-VOL and the remote copy is stored in the
S-VOL. The pair can be split, resynchronized, reverse resynchronized, and returned to unpaired
status.
•
When paired, the volumes are synchronized.
•
When split, new data is sent to the P-VOL but not the S-VOL.
•
When resynchronized, data that changed while the pair was split is copied to the S-VOL.
•
When necessary, data in the S-VOL can be copied to the P-VOL.
During normal operations, the P-VOL remains available to the host for read and write I/O operations.
The secondary system rejects write I/Os for the S-VOL. The S-VOL can only be written to when the
pair is split and when the write-enable option is specified for the S-VOL. In this instance, S-VOL
and P-VOL track maps keep track of differential data and are used to resynchronize the pair.
Data path
Continuous Access Synchronous operations are carried out between primary and secondary storage
systems connected by a Fibre Channel interface. The data path, also referred to as the remote
copy connection, connects ports on the primary XP7 storage system to the ports on the secondary
storage system. The ports are assigned attributes that allow them to send and receive data.
One data path connection is required, but two or more independent connections are recommended,
for hardware redundancy.
Consistency groups
A consistency group is a grouping of pairs upon which copy operations are performed
simultaneously, and in which the pairs' status remains consistent. A consistency group can include
pairs that reside in from one to four primary and secondary systems.
You can issue a Continuous Access Synchronous command to the consistency group so that it is
run on all pairs in the group. The pairs' statuses change at the same time, though this depends on
the group options you have set. Some pair operations take priority under certain circumstances.
Full information is covered in
“Consistency group planning” (page 24) .
Interfaces
You perform Continuous Access Synchronous operations using one of the following interfaces:
•
Remote Web Console, which is a browser-based interface from which Continuous Access
Synchronous is set up, operated, and monitored. The GUI provides the simplest method for
performing operations, requiring no previous experience.
◦ The primary system must be LAN-attached to a Remote Web Console computer.
◦ The secondary system should also be LAN-attached to a separate Remote Web Console
at the remote site. This allows you to perform operations more efficiently on the secondary
system in the event that the main site is not available.
•
RAID Manager, which is a command line interface used to display pair information and
perform all copying and pair-managing operations. RAID Manager provides a full scripting
capability that can be used to automate replication operations. RAID Manager is required for
performing failover operations.
Volume pairs 9