Chapter 3 Configuring Your Library
Working With FC I/O Blades
Scalar i500 User’s Guide
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to which it is attached. These LUNs can be re-mapped to new LUNs for
presentation via ports 1 and 2. Further, custom LUN maps can be
simultaneously defined for individual hosts.
For example, the I/O blade may discover tape drives attached to ports
3–6, each of which report themselves at LUN 0. The I/O blade could be
configured to re-map these to LUNs 1, 2, 3, and 4 for discovery on ports 1
and 2. If desired, they could also be simultaneously mapped to LUNs 3, 5,
7 and 9 for a specific host server.
There is also an internal (i.e., not attached to a port) controller device
presented at LUN 0 by default. The controller device facilitates
initialization and device discovery. In some instances it may be useful to
map the controller device to a different LUN if an application typically
expects to see a medium changer or tape drive at LUN 0.
LUNs can also be mapped to be accessible by specific host server World
Wide Port Name (WWPN). Mapping a LUN to a specific WWPN can be
used instead of channel zoning to control device visibility. Mapping a
LUN to more than one WWPN may be useful for creating redundant
paths to a medium changer, tape drive, or controller device. LUNs will
need to be mapped to each WWPN for host servers that use multiple
ports (e.g., multi-ported HBAs or multiple HBAs) if access is desired via
all the host server ports (e.g., a LUN would need to be mapped to both
WWPNs of a server that uses a dual-port HBA).
LUN masking is a complementary concept to host mapping in that LUNs
that are mapped to specific host server WWPNs are hidden (i.e., masked)
from other host servers. This is useful when more than one host server is
attached to the I/O blade (e.g., in a SAN). One or more of the LUNs can
be masked from discovery by specific host servers while maintaining
their mapping and accessibility to other host servers via the same port(s).
Host Mapping Vs.
Channel Zoning
3
Channel zoning places an operational restriction on mapped LUNs (for
example, if port 1 is zoned to ports 3 and 4, but LUNs from ports 3
through 6 have been mapped to a specific host server WWPN, the devices
on ports 5 and 6 cannot be accessed from that host via port 1, even though
they are mapped to it; only the devices on ports 3 and 4 would be
accessible from the host via port 1).
Host mapping can be used to control visibility of the medium changer
devices found on the I/O blade internal virtual port, while channel
zoning can be used to create simple access control to the other target
devices. If the host mapping capabilities are used to control visibility and
