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When OpenVMS is used with Fibre Channel disks, it requires a user-defined identifier (UDID) for each Fibre Channel LUN to detect and name the storage device.
A UDID is a non-negative integer that is defined on the storage sub-system and used when an OpenVMS device name is created.
This article describes the use of the user-defined identifier (UDID) in an OpenVMS environment. Charon products do not specify requirements regarding this value. The requirements are set by the OpenVMS operating system. |
Valid UDID values are decimal numbers from 0 to 32766.
If the Fibre Channel disk device is served via MSCP, the device identifier is limited to 9999. |
In addition to using a valid number, note that the UDID
The UDID may be configured to match the device LUN, but this is not a requirement. |
A Fibre Channel storage disk device name is created by the operating system from the constant value $1$DGA and the user-defined device identifier, nnnnn. For example: "$1$DGA512".
Fibre Channel disk device names always use an allocation class value of 1 (indicated by $1$). Fibre Channel tape device names use an allocation class value of 2 (indicated by $2$).
OpenVMS treats LUN 0 differently than other LUNs: for allocation class 1 (disk devices), LUN 0 is treated as the Command Console LUN (CCL). It is not displayed as a storage device but as $1$GGAnnnnn device. |
OpenVMS detects the UDID value of a device in one of two ways:
Storage sub-system support for opcode 0xEC is only necessary if Fibre Channel is attached via PCI pass-through and the device $1$DGA0 is required by the OpenVMS guest system. If Fibre Channel is virtualized, Charon provides support for the 0xEC command. |