Specifications

The access-restricted mode prevents all fibre-channel-attached host systems
that do not have an access profile from accessing any volumes that you have
defined in the ESS. This is the default mode.
Your IBM service support representative (SSR) can change the logical unit number
(LUN) access mode. However, changing the access mode is a disruptive process,
and requires that you shut down and restart both clusters of the ESS.
Access profiles
Any fibre-channel-attached host system that has an access profile can access only
those volumes that are defined in the profile. Depending on the capability of the
particular host system, an access profile can contain up to 256 or up to 4096
volumes.
The setup of an access profile is transparent to you when you use the ESS
Specialist to configure the hosts and volumes in the ESS. Configuration actions that
affect the access profile are as follows:
v When you define a new fibre-channel-attached host system in the ESS Specialist
by specifying its worldwide port name (WWPN) using the Modify Host Systems
panel, the access profile for that host system is automatically created. Initially the
profile is empty. That is, it contains no volumes. In this state, the host cannot
access any logical volumes that are already defined in the ESS.
v When you add new logical volumes to the ESS using the Add Fixed Block
Volumes panel, the new volumes are assigned to the host. The new volumes are
created and automatically added to the access profile of the selected host.
v When you assign volumes to fibre-channel-attached hosts using the Modify
Volume Assignments panel, the selected volumes are automatically added to the
access profile of the selected host.
v When you remove a fibre-channel-attached host system from the ESS Specialist
using the Modify Host Systems panel, you delete the host and its access profile.
The anonymous host
When you run the ESS in access-any mode, the ESS Specialist displays a
dynamically created pseudo-host called anonymous. This is not a real host system
connected to the storage server. It is intended to represent all fibre-channel-
attached host systems that are connected to the ESS that do not have an access
profile defined. This is a visual reminder to the user that certain logical volumes
defined in the ESS can be accessed by hosts which have not been specifically
identified to the ESS.
ESSESS
Fibre-channel storage area networks (SANs)
A SAN is a specialized, high-speed network that attaches servers and storage
devices. A SAN is also called the network behind the servers. With a SAN, you can
perform an any-to-any connection across the network using interconnect elements
such as routers, gateways, hubs, and switches. With a SAN, you can eliminate the
connection between a server and storage and the concept that the server effectively
owns and manages the storage devices.
The SAN also eliminates any restriction to the amount of data that a server can
access. This is limited by the number of storage devices, that can be attached to
the individual server. Instead, a SAN introduces the flexibility of networking to
enable one server or many heterogeneous servers to share a common storage
Chapter 1. Introduction 17