Storage Area Networks For Dummies®

Chapter 7: Put ting It All Together
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One more concept to understand is the session — the two-way traffic between
specific initiator and target pairs. Each session is unique to help ensure that
data coming and going across your network ends up in the right place.
When a session is established between the initiator and target, you have an
open communication link to get information back and forth, just like an open
phone connection between you and grandma.
IQN: iSCSI qualified name
Remember the concept of World Wide Names? Each port on a Fibre Channel
SAN, whether it was an HBA or a storage port, has a unique number. iSCSI also
requires unique names, but it uses a less cryptic and more descriptive way to
keep things straight. This is the concept of an iSCSI Qualified Name, or IQN.
The software that manages the iSCSI initiator automatically creates an IQN
for you. You can change it to something else if you want to micromanage
your iSCSI SAN. However, if you rename your host, the IQN probably will
change as well. This could affect any drive mappings made previous to the
host name change.
Each storage target on the iSCSI network also has a unique IQN, which usually
has the vendor and serial number of the storage array embedded in it.
The idea is to make sure each one is always unique.
SCSI Name Service
So you have all these IQNs now. How do you keep them organized and use
them wisely? The answer is a SCSI Name Service server. This server is a
computer on your network that all the iSCSI devices say “hello” to when they
start up. The “hello” message is a registration of the IQN into a master list
that you can use to match up your initiators and targets.
Microsoft uses a service for their users called iSNS. It allows initiators and
targets to register and be managed centrally. Most other operating systems,
such as Unix, Linux, and Mac OSs, have similar ways to manage iSCSI names.
The best thing about SNS servers is that now you have a central way to see
and control your iSCSI initiators, which otherwise would be randomly looking
around the network for targets to talk to. This is where the concept of a data
domain comes in handy.