Clarification on the assigning of the allocation class descriptor on an EVA disk drive, eg $1$DGA50:

[Andrew Rycroft]

Hi,

Is it possible someone can help me clarify where the allocation class descriptor is defined for the EVA disk drive ?

From VMS I do a $ SHOW DEVICE $1$DGA50:

I know where the 50 comes from, but I cannot seem to find anywhere in the documentation where the $1$ is defined. It is not the ALLOCLASS SYSGEN parameter under OpenVMS.

Appreciate any assistance.

With regards
Andrew

[Ian Miller. · Accepted solution]

fibre chan disks allways get allocation class 1

[Uwe Zessin]

As Ian has already written, this is hard-coded in the driver. The CCL (LUN #0), if it is assigned an identifier, also uses allocation class 1 ($1$GGAu:).

The nice thing is that this automatically works for volume shadowing, which requires each disk to have an allocation class.

And we are lucky, because the MSCP server no longer requires that the host allocation class must be the same as the attached device to be served - it is amazing how VMS has evolved over time and still works ;-)

Tape devices, on the other hand, use allocation class 2 ($2$MGA3:) and
a controller LUN uses $2$GGAu:. You can not set identifiers on tape devices,
so this is controlled by a file (SYS$COMMON:[SYSEXE]SYS$DEVICES.DAT), if I
recall correctly - see 'SYSMAN IO FIND_WWID', if you are interested.