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MPE/iX makes a distinction between the device and the media.
The device is the disk drive and the media is the disk pack. The
MPE/iX volume management facility controls the media and divides
the media into three entities:
Volume set, a set of related disk packs assigned to the group in
which you create your file. Volume class, a subset of a volume set. A volume
can be assigned to more than one volume class. Volume, a single disk pack. Each volume on a system
is a member of a volume set.
By default, when you create (or otherwise access) a disk file and data is
posted to disk, new extents are placed wherever space is available on any
volume within the volume class DISC assigned to the group in which
your file resides.
You can use either the volume name option or the
volume class option of HPFOPEN, or the
device parameter of FOPEN, to specify either a volume
name or a volume class name, thus restricting the placement of your file's
extents to either the specified volume or to the specified volume class within
the volume set.
The device parameter of FOPEN also allows you to
specify a volume name or a volume class in an additional manner, due to the
necessity of maintaining FOPEN compatibility with MPE V/E based
computer systems. If an LDEV (a logical device number used to identify a
device) is passed into FOPEN, MPE/iX translates the LDEV into the
volume name that is currently mounted on the disk device and places the volume
name in the file's label. Similarly, a device class that is associated
to a disk device is translated into the volume class name.
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NOTE: HPFOPEN fails if, when creating a disk file, an LDEV is
passed to volume name option for a mounted disk or a device
class is passed to volume class option.
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