Jukebox Management Software
by Lowell Rapaport
The most fundamental purpose of jukebox management software is to provide drive letter access to a jukebox. This lets applications and users directly access the jukebox without having to use some exotic programming. Jukeboxes are too complex for the standard computer desktop, so management software simplifies the manner in which users gain access to jukeboxes for storing and retrieving files.
There are two ways in which drive letters are assigned to disc volumes inside a jukebox. One way is for the jukebox management system to make the entire jukebox appear as a single drive letter. Each disc in the jukebox appears as a folder. From the Windows interface, you can then assign drive letters to groups of folders. Ixos' Jukeman provides drive letter access this way. A second way is to create groups of discs within the jukebox management system and assign drive letters to each group. The latest version of KOM's Optistorm lets you create such "virtual discs.' The former method has the advantage of giving you almost universal flexibility in grouping discs together. You are limited only by Windows' ability to group files and folders. The latter lets you build drive letter access without having to mount the whole jukebox to the network, exposing some data to security risk.
The jukebox management system must keep a directory of all the files contained within the jukebox. That directory is stored in a database. Usually, specialized proprietary databases are used. Ixos, Pegasus and Tracer all use their own databases specially designed for their jukebox managers. Kofax's Ascent Storage and Smart Storage's SmartCD use Btrieve, a database specially designed for embedded applications like jukebox management or COLD.
Occasionally, an "off-the-shelf" database serves as the filing system for the jukebox software. Older versions of OTG's DiskExtender used an ordinary SQL or Oracle database, but the latest version abandons off-the-shelf databases in favor of Windows NT's built-in filing system, NTFS. KOM's Optistorm also uses NTFS.
Since jukeboxes are relatively slow as compared to RAID or local hard drive storage, jukebox management software employs tricks to boost performance. For instance, many systems analyze the request queue and group together file requests that are from the same disc. This prevents disc thrashing, a condition where a single disc is constantly mounted and unmounted as files from the disc are called up. Disc thrashing wastes time and can prematurely wear out the jukebox robotics and drives.
When you have a large number of users trying to access a jukebox all at once, it can take a frustratingly long time for users to gain access to their files. To address this problem, jukebox software developers create caching schemes where recently retrieved files are stored, temporarily, on a server's hard disc. Caching can also be enhanced through pre-fetching. With pre-fetching, the management system tries to predict which file the user will request next and cache that file as well. Pre-fetching is hard to implement. Too much pre-fetching will waste time and too little will not improve performance.
Jukebox management systems generally come in two parts. (The only exception to this design in this review is Pegasus Investore, which combines the jukebox manager and the administrator). The jukebox manager runs continuously on top of the operating system and operates the jukebox. The second part is the jukebox administrator, which serves as a control panel for the jukebox manager. The administrator lets the user add and remove discs, move discs from one location to another, and manage caching, file migration and other jukebox functions. The jukebox administrator does not have to run continuously. Nor does the administrator have to run on the jukebox server. This permits remote administration of a jukebox from a workstation.
-- Lowell Rapaport
Source: Transform Magazine