Accessing Files Programmer's Guide (32650-90885)

Chapter 2 63

Creating A File

Specifying Disk Volume Restrictions

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.

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