HP StorageWorks XP Remote Web Console Software - Manual (Page 26)

Data Volume Pair
URz performs remote copy operations for data volume pairs created by the user. Each URz pair consists
of one primary data volume and one secondary data volume which can be located in different storage
systems. The URz primary data volumes are the primary volumes (LDEVs) which contain the original
data, and the URz secondary data volumes are the secondary volumes (LDEVs) which contain the
backup or duplicate data. During normal URz operations, the primary data volume remains available to
all hosts at all times for read and write I/O operations. During normal URz operations, the secondary
storage system rejects all host-requested write I/Os for the secondary data volume. The secondary data
volume write enable option allows write access to a secondary data volume while the pair is split
and uses the secondary data volume and primary data volume track maps to resynchronize the pair
(see“ Secondary Data Volume Write Option ” on page 36).
URz also supports the Virtual LVI/LUN (VLL) and Cache Residency Manager features, so that URz meets a
variety of user needs and facilitates data copying and data migration. This ensures that all user data
can be backed up or duplicated. See “ Duplicate VOLSER (Volume Serial Number) ” on page 57 for
further information on LU requirements and support.
Journal Volume
When URz is used, updates to primary data volumes can be stored in other volumes, which are called
journal volumes. The updates (which are sometimes referred to as update data) that will be stored in
journal volumes are called journal data.
Because journal data will be stored in journal volumes, you can perform and manage highly reliable
remote copy operations without suspension of remote copy operations. For example:
Even if a communication path between the primary storage system and the secondary storage system fails
temporarily, remote copy operations can continue after the communication path is recovered.
If data transfer from hosts to the primary storage system is temporarily faster than data transfer between
the primary storage system and the secondary storage system, remote copy operations between the
primary storage system and the secondary storage system can continue. Because journal volumes can
contain a lot more update data than the cache memory can contain, remote copy operations can
continue if data transfer from hosts to the primary storage system is faster for a relatively long period of
time than data transfer between the primary storage system and the secondary storage system.
The Number of Journal Volumes
One journal group can contain up to 64 journal volumes. Each of the journal volumes can have different
volume sizes and different RAID configurations. Journal data will be stored sequentially and separately
into each journal volume in the same journal group.
Specifications of Journal Volumes
• Types of logical units (LUs):
The following DKU emulation types are allowed for journal volumes:
Table 2 Emulation Types for Journal Volumes
Emulation Category Supported Emulation Types
• OPEN-V DKU (drive)
• All mainframe volumes that can be used with XP disk array
NOTE:
Status of mainframe volumes cannot be referenced.
• Volumes and their capacity:
You can use VLL volumes for journal volumes.
26 Overview of Universal Replicator Operations