Offline storage is data that you save on media that is separate from the server.
The most common forms of offline storage are tape media and optical media. Although optical media is becoming more prevalent, tape media is the most common media. Another option that you can use is virtual optical media. You can use virtual optical media to save to a virtual image, which is stored on your disk units. You can then copy that image to a CD or DVD, or distribute it over your network.
It is important that you understand the differences among these different forms of media while you decide which one is right for you. The following table describes some of the differences:
| Characteristic | Comparison |
|---|---|
| Access to data | Optical and virtual optical storage provide random access, whereas tape provides access to data sequentially. |
| Capacity | The lowest capacity tape has a similar capacity to DVD-RAM, but midrange and high capacity tapes typically have 10 to 25 times the capacity of optical. |
| Compression | The server uses software compression to save compressed data to your optical media. This process takes considerable processing unit resources and may increase your save and restore time. Most tape media devices use hardware compression, which is typically faster. |
| Cost | Because you can store a larger amount of data on tape, tape has a lower cost per gigabyte. |
| Data transfer rates | Data transfer rates for tape tend to be higher than for optical media, particularly if you use tape drive compression. |
| Number of media passes or mounts | Optical media can be mounted anywhere from 50 000 to 1 million times, depending on the type of media used. The number of media passes supported by tape varies, but is typically lower than optical media. |
| Reusability | Not all optical media is rewritable. Some optical media are write-once media, which means that once they are written to, they cannot be reused. Tape is reusable. |