Chapter 2. System overview 35
In the simplest terms, iSCSI enables the transport of SCSI commands and data over an 
Internet Protocol network, based on IP routers and Ethernet switches. iSCSI is a block-level 
protocol that encapsulates SCSI commands into Transmission Control Protocol/Internet 
Protocol (TCP/IP) packets and uses an IP network, rather than requiring expensive FC host 
bus adapters (HBAs) and a SAN fabric infrastructure.
The major functions of iSCSI include encapsulation and the reliable delivery of CDB 
transactions between initiators and targets through the Internet Protocol network, especially 
over a potentially unreliable IP network.
Every iSCSI node in the network must have an iSCSI name and address. Consider the 
following points:
/SM590000An iSCSI name is a location-independent, permanent identifier for an iSCSI node. An 
iSCSI node has one iSCSI name that stays constant for the life of the node. The terms 
initiator name and target name also refer to an iSCSI name.
/SM590000An iSCSI address specifies not only the iSCSI name of an iSCSI node, but a location of 
that node. The address consists of a host name or IP address, a TCP port number (for the 
target), and the iSCSI name of the node. An iSCSI node can have any number of 
addresses, which can change at any time, particularly if they are assigned by way of 
Dynamic Host Configuration Protocol (DHCP). An IBM SAN Volume Controller node 
represents an iSCSI node and provides statically allocated IP addresses.
2.5.20  Real-time Compression
IBM Real-time Compression is an attractive solution to address increasing data storage 
requirements for power, cooling, and floor space. When applied, IBM Real-time Compression 
can significantly save storage space because more data is stored in rack space so fewer 
storage enclosures are required to store a data set. IBM Real-time Compression provides the 
following benefits:
/SM590000Compression for active primary data. IBM Real-time Compression can be used with active 
primary data. 
/SM590000Compression for replicated/mirrored data. Remote volume copies can be compressed in 
addition to the volumes at the primary storage tier. This process also reduces storage 
requirements in Metro Mirror and Global Mirror destination volumes. 
/SM590000No changes to the environment are required. IBM Real-time Compression is part of the 
storage system.
/SM590000Overall savings in operational expenses. More data is stored in a rack space, so fewer 
storage expansion enclosures are required to store a data set. This reduced rack space 
has the following benefits:
– Reduced power and cooling r equirements. More data is stored in a system, which 
requires less power and cooling per gigabyte or used capacity.
– Reduced software licensing for more functions in the system. More data stored per 
enclosure reduces the overall spending on licensing.
/SM590000Disk space savings are immediate. The space reduction occurs when the host writes the 
data. This process is unlike other compression solutions, in which some or all of the 
reduction is realized only after a post-process compression batch job is run.