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VMware ESX Server Administration Guide
The DiskMaskLUNs configuration option allows the masking of specific LUNs on
specific HBAs. Masked LUNs are not touched or accessible by the VMkernel, even
during initial scanning. The DiskMaskLUNs option takes a string comprised of the
adapter name, target ID and comma-separated range list of LUNs to mask. The format
is as follows:
<adapter>:<target>:<comma_separated_LUN_range_list>;
For example, you want to mask LUNs 4, 12, and 54-65 on vmhba 1 target 5, and LUNs
3-12, 15, and 17-19 on vmhba 3 target 2. To accomplish this, set the DiskMaskLUNs
option to the following:
"vmhba1:5:4,12,54-65;vmhba3:2:3-12,15,17-19;"
Note: LUN 0 cannot be masked.
The DiskMaskLUNs option subsumes the DiskMaxLUN option for adapters that have a
LUN mask. In other words, continuing the preceding example, there are four adapters,
vmhba0, vmhba1, vmhba2, and vmhba3, and the DiskMaxLUN option is set to 8. In
this example, vmhba0 and vmhba2 only scan LUNs 0-7, but vmhba1 and vmhba3
scan all LUNs that are not masked, up to LUN 255, or the maximum LUN setting
reported by the adapter, whichever is less.
For administrative or security purposes, you can use LUN masking to prevent the
server from seeing LUNs that it doesn’t need to access. Refer to your documentation
on disk arrays for more information.
Using IBM FAStT Disk Arrays
An IBM FAStT disk array sometimes returns vendor-specific status codes that ESX
Server interprets as errors. These status codes are temporary -- indicating, for example,
that the firmware has been upgraded or that the battery for the disk cache needs to
be charged. ESX Server, in its default configuration, may interpret these status codes
to mean that a LUN exists but is not accessible.
You avoid this problem by using a special ESX Server configuration option. Log in to
the management interface as the root user, click Advanced Settings, then click
VMkernel Configuration. Find the option DiskRetryUnitAttention and be
sure that it is enabled (the default).
With this option enabled, ESX Server automatically retries SCSI commands when
these vendor-specific status codes are received.