HP-UX System Administrator's Guide: Overview

protection. Storage Area Networks work at the block I/O layer, below the file
system layer.
• Network Attached Storage (NAS), an alternate network storage solution, working
at the file system layer using standard network protocols (NFS, CIFS)
• Off line storage or removable media. Data are stored on:
— Tapes (DLT, DDS, Reel, and other tape formats)
— Optical Media (CD, Magneto-optical, DVD-ROM, and other optical formats)
— Removable disk drives
Offline storage is often used for off site storage of data (usually backups) for
purposes of disaster recovery.
Storage Uses
In the HP-UX operating system, storage can be used in many ways; among them:
• Files and Directories stored locally in file systems
• Databases stored on disk volumes in raw form (managed by the database
application rather than by HP-UX) for speed
• Swap space (used by HP-UX for paging purposes)
• Dump space (used to capture the state of HP-UX following a system panic or other
significant event)
How Storage is Organized
Like networking and many other subsystems in the computing world, storage is
comprised of many layers, from the physical devices to the applications that read and
write data to those devices. Collectively these layers are known as the storage stack.
The following sections cover the various components of the HP-UX storage stack.
Physical Storage Devices
At the lowest level of the storage stack are the physical devices that store and retrieve
data. Usually these are disk drives, but they can be other storage devices as well,
including:
• DLT tape drives / libraries
• Magneto-optical drives / libraries
• DDS tapes
Disk drives can be:
• Individual drives
• Drive enclosures (groups of multiple disk drives that are treated as individual
drives)
• Disk Arrays (like drive enclosures but with an added disk controller for local
intelligence in managing the contained storage (for example, RAIDs)
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