HP NonStop G-Series - Manual (Page 27)

Introduction to Storage Management
HP NonStop Storage Management Foundation User's Guide—523562-008
1-5
Virtual Disks and Physical Volumes
Any number of storage pools can be created dynamically on a system as needed.
File Placement and Organization
Files are placed by SMF on any physical disk volume in the pool. The specific physical
volume on which a file is placed is known to the disk process and SMF, but is not
apparent to the user and to applications.
System administrators and operators can define multiple storage pools with different
attributes to help organize the files on a system. For example, one pool on a system
could be devoted to a development group, while another pool could be assigned to a
production group. Storage pools must also have different storage functions. For
example, one pool could be used for active files, and another pool could be used for
archiving inactive files.
Virtual Disks and Physical Volumes
As there are logical and physical file names, so are there virtual disks and physical
volumes. A virtual disk appears to application programs to be a physical volume in
almost all respects. The key difference between virtual disks and physical volumes is
that, unlike a physical volume, a virtual disk does not correspond to a physical device.
Any number of virtual disks can be associated with any number of physical volumes.
Files on virtual disks are not necessarily placed by SMF on a single physical volume.
The relationship between virtual disks and physical volumes can be summarized in
these ways:

There might be one physical volume and 12 virtual disks in a pool. The 12 virtual
disks might be assigned to 12 members of a development group who share space
on the single physical volume.

There might be 100 physical volumes and 10 virtual disks in a pool. A single
physical volume might hold files from all 10 virtual disks, and the files on a single
virtual disk might reside on all 100 physical volumes.

There might be one virtual disk and multiple physical volumes used; for example,
for temporary space management.
Figure 1-1 illustrates the concept of virtual disks within a storage pool and the
relationships of physical volumes to virtual disks.