SCF Reference Manual for the Storage Subsystem (G06.27+, H06.04+)

Configuring and Managing Virtual Disks
SCF Reference Manual for the Storage Subsystem—529937-008
10-2
Overview of Virtual Disks
Overview of Virtual Disks
To understand virtual disks:
•
How Virtual Disks Relate to Magnetic Disks on page 10-2
•
Functions of the Virtual Disk Process on page 10-2
•
Location-Independent Naming on page 10-2
How Virtual Disks Relate to Magnetic Disks
A virtual disk appears to application programs to be a magnetic disk in most respects.
However, some SCF commands affect only magnetic disks, not virtual disks, and other
commands affect only virtual disks, not magnetic disks.
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 magnetic disk. The following examples
summarize the relationships between virtual disks and magnetic disks:
•
One physical volume might be 12 virtual disks, allocated to 12 users who share
space on the same disk.
•
Fifty magnetic disks might be 10 virtual disks, allocated to 10 users requiring a
large amount of storage for completing their development work.
•
Five magnetic 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 magnetic 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.