Chapter 2 About Universal Replicator Operations 2-11
Hitachi Universal Replicator for IBM /OS User’s Guide
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 2-1 Emulation Types for Journal Volumes
Emulation Category Supported Emulation Types
DKU (drive)
OPEN-V
All mainframe volumes that can be used with USP V
Note: Status of mainframe volumes cannot be referenced.
Volumes and their capacity:
You can use VLL volumes for journal volumes.
Journal volumes in the same journal group can be of different capacity. A
master journal volume and the corresponding restore journal volume can
be of different capacity.
