Hitachi MP-96RD625-01 manual Journal Obtain, UR Components for Fibre-Channel Connection

Primary site

Primary host

Secondary site

Secondary host

Write instruction

		Issuing Read
Primary		Journal command		Secondary
data				data
volume		Journal copy function		volume
	Master		Restore
Journal obtain	journal		journal	Journal restore
function	volume		volume	function
Primary storage system			Secondary storage system

Figure 2-1 UR Components for Fibre-Channel Connection

Journal Obtain

Journal obtain is the function to store the already stored data in the primary data volume as a base-journal in the journal volume at the primary site. And then, this function stores the write data as a journal data in the journal volume with every update of the primary data volume according to the write instruction from the host. The journal obtain operation is performed according to the instruction of add pair or Resume Pair operation from the primary site. The write sequence number from the host is assigned to the journal data. According to this information, the write sequence consistency at the secondary site can be maintained. The update data from the host is kept in the cache. Therefore, the journal obtain function for the update data is performed asynchronously from the time the storage system receives the update data from the host and stores the update data to the data volume.

Chapter 2 About Universal Replicator Operations 2-3

Hitachi Universal Replicator for IBM /OS User’s Guide