Virtual DVD Server - CDH

What is the Virtual DVD Server?
The Virtual DVD Server is a caching CD/DVD server. It is used to copy CD/DVD data onto a hard drive, or hard drive array. What does this mean and what benefits does it create?

Caching is another word for copying. Hard drives respond faster than CD/DVDs to requests for data. So copying CD/DVD data to a hard drive decreases user wait-time and increases productivity.

Hard drives can store much more information than a physical CD/DVD. Previously, an array of CD drives called a CD Tower was needed to search across multiple CD-ROMs. But each drive required an assigned drive letter, or mapping. In a Windows environment this meant that a maximum of 23 CD-ROMs could be accessed.

CD Towers were usually attached to network file servers. This created a high "load" on the file server; draining resources that were needed for other network tasks. Moving the CD/DVD resources to a Virtual DVD Server removes the "load" from the file server; making the file server resources more available.

Why "Virtual"? The name refers to the fact that the system stores the CD/DVD data, but the physical CD/DVD disc is not used. The caching process creates images of CD/DVDs, or "Virtual CD/DVDs".

Caching Levels
The Virtual DVD Server uses three different levels of CD/DVD access: Direct Access, Performance Caching, and Mirror Images. Each provides a different level of speed and permanence for the network user.

Direct Access
The title of this access level is self-explanatory. When a CD/DVD drive is set for Direct Access the CD/DVD inserted into the drive it is not copied to the hard drive, but can be immediately employed by network users. When the CD/DVD is removed from the drive it is not longer accessible. The benefit is the ease of administration - just insert the CD in the drive. But the response time for user requests depends on the speed of the physical CD/DVD drive.

All Direct Access CD/DVDs are available to network users by mounting/mapping the CDROMS volume of the Virtual DVD Server.

Performance Caching
A performance cache is a temporary copy of CD/DVD data to a hard drive. Network users requesting data from the CD/DVD actually receive the response from the hard drive copy: increasing response time. The copy only exists as long as the physical CD/DVD remains inserted in the drive. When the CD/DVD is removed from the drive, the cache is automatically deleted. The benefit of a performance cache is the increased response time, without the maintenance of tracking and deleting an "old" virtual CD.

All Performance Cached CD/DVDs are available to network users by mounting/mapping the CACHE volume of the Virtual DVD server.

Mirror Images
A Mirror Image is a permanent copy of a CD/DVD: a virtual CD/DVD. This is the most common cache created on the Virtual DVD Server. A mirror image will not be deleted when a CD/DVD is ejected from the drive bay. It will provide fast network response to requests.These two phrases, mirror and image, are used interchangeably in this book.

All Mirror Images are available to network users by mounting/mapping the MIRROR volume of the Virtual DVD Server.