One of the biggest considerations when changing to a new backup medium, such as a different tape format, is converting the existing archive and backup files. How much of a problem this is depends on several factors -- and how you choose to approach it.
The most common conversion is probably going to a later generation of the medium, such as DLT, that you have been using to get more capacity or speed. Since most media are compatible at least one or two generations back, you can choose to leave your archived material on the old format and accept slower access speeds and smaller tape capacities for the existing tapes.
One important factor is how much material you have to convert. If you're dealing with a pure backup medium, the amount will be fairly minimal. If you have archived material on tape, especially if you are using a hierarchical storage management (HSM) system, there are more tapes to convert. However if the archived material is accessed at all frequently, you may want to convert it to the newer format both to speed access and simplify managing the library.
If you decide to completely convert your media, there are several ways to do it. Reading the old tapes into a system and immediately dumping the material onto new media works, but it can be a cumbersome process -- especially with modern storage systems.
If you have more than a minimal number of tapes, you will probably want to look at investing in software specifically designed to convert media, such as MediaMerge from eMag Solutions. These packages will help smooth the conversion, along with arranging and cataloging the old material appropriately onto the new medium.
An alternative, especially if you have a lot of archived material, is to pay someone else to do it for you. There are a number of services specializing in media conversion, such as Universal Conversion Services Inc. (UCSI). These companies can typically convert data as well, such as translating EBDIC data into ASCII.
Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.