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Well don't know what program/method you are planning to use but with Toast anyway it is a simple matter of duplicating the Toast program and then running both copies. Each can then be dedicated to burning to each drive. Not all programs will allow this but Toast has had that functionality since at least Toast 8 and I will assume earlier as well.

If you are just planning to burn from the finder, there is no issue with that either. Just stick in two blanks and they will show up as burn folders on the desktop.
 
Let me further explain my question. How would I go about backing up say a 15GB file with a software that automatically splits and copies to both superdrives... simultaneously.
 
Let me further explain my question. How would I go about backing up say a 15GB file with a software that automatically splits and copies to both superdrives... simultaneously.
Yeah that is indeed different. While, again using Toast for an example, some programs do feature the ability to write data to multiple disks (use "disk spanning mac" for a Google search term) I have never heard of one that would write the parts simultaneously.

There also are some programs out there that will allow you split a file up into chunks but all that I have ever seen limit the maximum file size to 2Gb due to an OS constraint so your theoretical 15Gb file would still wind up in 8 chunks.

Since the vast majority of Macs don't even have two optical drives I really think that a program capable of spanning to multiple disks is as close as you are going to get.
 
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