SCF Reference Manual for the Storage Subsystem (G06.28+, H06.05+, J06.03+)

Any number of virtual disks can be associated with a pool. The files on a virtual disk are not
necessarily placed by SMF on a single physical disk. The following examples summarize the
relationships between virtual disks and physical disks:
• One physical volume might be 12 virtual disks, allocated to 12 users who share space on the
same disk.
• Fifty physical disks might be 10 virtual disks, allocated to 10 users requiring a large amount
of storage for completing their development work.
• Five physical disks might be one virtual disk, as one way of handling temporary space
management.
Functions of the Virtual Disk Process
The virtual disk process:
• Performs file placement management; that is, the mapping between external and internal file
names that supports location-independent naming
• Maintains a name catalog that contains the name-mapping information between the external
and internal names of files that reside on the physical volumes it uses
• Gathers statistical information on the status of physical disks in the storage pool so you can
determine the best location for the files on the disks
Location-Independent Naming
Virtual disks take advantage of location-independent naming. As a result, a file’s external or logical
name can differ from its internal name. In earlier RVUs, the external file name indicated the physical
location of the data; that is, each file name indicated the node, volume, and subvolume where the
file was located. For example, the file OVERDUE on system \SYSA, volume $DATA00, and
subvolume CURRENT, is named \SYSA.$DATA00.CURRENT.OVERDUE.
With location-independent naming, the file \SYSA.$DATA00.CURRENT.OVERDUE can reside on
any physical volume. With the exception of the node name, the name of the file managed by SMF
is independent of its location.
SMF controls the mapping of the external name to the internal name. The internal name, which
identifies the file’s physical location, can change when a file is moved to a different location, while
the external name remains the same to applications.
Displaying Information
To display information about virtual disks:
• “Displaying Configuration Information for Virtual Disks” (page 144)
• “Displaying Current Status Information” (page 146)
Displaying Configuration Information for Virtual Disks
The “INFO DISK Command” (page 254) displays information about a virtual disk, as recorded in
the system configuration database.
Considerations for INFO DISK and Virtual Disks
• If the SMF master process ($ZSMS) is not started, the Configuration State in the INFO report
shows that the “SMF master process is Down.”
• If a configuration record for a virtual disk exists, but the SMF master process does not have
a definition for it, no information is displayed for attribute values that are supplied by the SMF
master process (the Configuration State in the INFO report displays “No Definition with SMF
master process”).
144 Configuring and Managing Virtual Disks