How does a backup product get a Very Large Database ( VLDB) or Very Large System (VLS) onto backup media? This is a slightly different scenario than the one described previously. The many-to-one concept is trying to deal with the fact that there may be thousands of clients but only a few backup drives. Many-to-one parallelism allows 5 or 10 systems to share the same device, so that backup devices are constantly streaming, and backups can be done in a timely manner. In contrast, the situation that calls for one-to-many is a single system that could not possibly back up its files to a single backup drive in one night. Even if one had a backup drive that is capable of 20 MB/s, that is only 72 GB per hour, or 576 GB in an eight-hour period—assuming the drive could be streamed for that long. What if the system contains 6 TB of data? Also, what if the drive is capable only of 5 MB/s? That backup drive could do only 144 GB in an eight-hour period.
The only way to get that kind of speed is to use four 20 MB/s drives simultaneously. (Other combinations would work, of course, but they all require multiple simultaneous backup drives.) However, in order to make that happen, the backup software needs to be able to take the one system and send it to many devices simultaneously. There are many products that are able to do this. What is important is how they do it.
There are two ways to accomplish the one-to-many requirement.