Silicon Graphics TP9100, Installation Instructions And User Manual

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Configuration Functions
007-4382-002 79
If IRIX or Linux computers are involved, then an automatic mount might not occur, but
you still have a security risk, and the possibility that a user with root privilege will mount
one of these disks, or attempt to create a file system on one of these disks.
By utilizing SAN mapping, however, each logical drive can be configured to be visible to
a single host computer only. If you are using a volume mapping tool such as Veritas’
Volume Manager, or Tivoli’s (previously Mercury’s) SANergy product, then you can
safely concurrently mount file systems on these LUNs to any number of these three hosts.
The controller uses the World Wide Name (WWN) to uniquely identify host computers
that have logged in to the controller. A list of valid hosts and their corresponding WWNs,
is provided to external configurators in order to configure the mapping.
After logical drives are configured, the controller maintains a table of WWNs for each
one. This table defines the hosts that are granted access to each system drive and the
controller port and the LUN number. The controller uses the table of WWNs to determine
access to a specific system drive. If a host sends a new command to the controller, the
controller validates the WWN, LUN, and controller port prior to servicing the command.
If the WWN, LUN, and port information are valid for the system drive, the requested
command is completed normally. If the WWN, LUN, and port combination are not valid
for the system drive, the command is completed with SCSI Check Condition status, with
the sense key set to Illegal Request (05h) and the sense code set to Logical Unit Not
Supported (25h).
There are three exceptions to the response to commands when the WWN, LUN, and port
combination are not valid:
1. If the request is an Inquiry command, the controller returns the Inquiry data with
the peripheral qualifier set to indicate that the target is capable of supporting the
specified device type on this LUN, but no device is currently connected to that
LUN.
2. If the request is a Report LUNs command, and the addressed LUN is 0, the
controller completes the command normally, reporting only the LUNs accessible by
the host requesting the command.
3. If the request comes from TPM, however, the command is processed normally by
the controller. This allows a controller that is not configured to be reconfigured to
operate correctly with the attached hosts.