/SIZE=n

    When /SIZE=n is specified for a magnetic disk, n specifies the
    size (in blocks) of the logical volume (the space available for
    the file system). This allows you to INITIALIZE a disk with a
    file system size that is less than the physical volume size,
    which can be useful if you plan to create a shadow set using this
    disk and a smaller physical disk. The value of n is displayed
    (in blocks) as "Logical Volume Size" in the output from a SHOW
    DEVICE/FULL command.

    For DECram disks, /SIZE specifies the size (in blocks) of the
    disk (device type DT$_RAM_DISK) to be allocated from available
    memory. The size of the device is created at disk initialization
    time.

    To deallocate space, specify /SIZE=0. All resources specifically
    allocated to the DECram disk are returned to the system.

    Note that n cannot exceed 524,280 blocks on versions of DECram
    prior to Version 2.3. DECram Version 2.3 running on an Alpha
    system supports up to 67,108,864 blocks, equivalent to 32GB.