HP XP Racks - Manual (Page 33)

The primary storage system suspends a pair when the following conditions occur:
•
The user has released the pair from the secondary storage system.
•
An error condition related to the secondary storage system, the S-VOL, or the update copy
operation.
•
Communications with the secondary storage system have stopped.
When a pair is suspended, the primary storage system stops sending updates to the S-VOL, even
though host applications may continue updating the P-VOL. The primary storage system records
the P-VOL's updated tracks as differential data. This data is copied to the S-VOL when the error
condition is cleared and the pair is resynchronized.
P-VOL/S-VOL differential data is not retained if a primary or secondary storage system is powered
off and its backup batteries are fully discharged while the pairs are suspended. In this unlikely
case, the primary storage system performs the equivalent of an entire initial copy operation when
the pairs are resynchronized.
For descriptions of suspend types and the troubleshooting steps to resolve them, see “Suspended
volume pair troubleshooting ” (page 73) .
Volume pair creation
A volume pair consists of primary and secondary volume whose data is synchronized until the pair
is split. During the initial copy, the P-VOL remains available to the host for read/write.
Creating an ESAM pair
There are two basic steps involved in creating an ESAM pair. They are:
•
Performing the initial copy.
•
Verifying that the host recognizes both the P-VOL and S-VOL as a single volume.
Prerequisites
Make sure you have configured the pair (see “System configuration” (page 21) ).
Procedure
When creating the pair, make sure that:
•
LDEVs for the primary and secondary volumes:
Are created and formatted. ◦
◦ Have identical block counts.
◦ Are in SMPL status.
•
The S-VOL must be offline; the P-VOL can be online.
•
You copy each volume's port number, host group number (GID), and LUN. This is needed
during the procedure.
•
You copy the CU Free RCU from which you will assign the secondary volume. Copy the serial
number, LDKC number, controller ID, model name, path group ID, and the channel type.
•
You assign a quorum disk to the ESAM pairs during the initial copy procedure. The pairs
created between the same primary and secondary storage system must be assigned the same
quorum disk.
Volume pair creation 33