There must be a volume to store data that the applications read for processing. To allocate a volume to a transaction server, it is necessary to create the required disk space from a disk unit. Therefore, a storage administrator estimates the disk size required for each transaction server and creates a logical unit according to the estimation.
Virtual Storage is a function that enables the creation of a volume with any disk size, independently of the attributes (e.g., size, RAID group) of logical units created on a disk unit.
In a Storage Area Network (SAN) environment, the Virtual Storage function is provided through the following three layers.
Figure 1.1 Layers in which Virtual Storage is realized
The server layer provides an application with virtual storage by operating virtual storage software on the transaction server where the application runs.
The network layer places a special server dedicated for the virtual storage function between the transaction server where an application runs and a disk unit. This special server provides a logical unit allocated from the disk unit to the transaction server as virtual storage.
The storage layer provides a disk unit as a logical unit that does not depend on the RAID group function or the hard disk drive size.
