[l008com]

Is there a way to do this in OS X? I'm not talking about a RAID. What I need to do is take a 3 TB drive and a 0.5 TB drive, and span them into a single 3.5 TB volume. Then I need to make a very large database on that volume, that when done, will take up a hair under 3 TB. Then I need to un-span the volume and remove the 500 GB drive.

Is this something you can do on OS X with disk utility? Or with any 3rd party programs?

The deal is that I'm making a few VERY large mysql databases, and I want each one to fill a drive. But in the process of indexing these tables, you end up needing a lot of extra space. But once the indexes are made, you get that space back. Since I don't have any 4TB drives lying around, making it on one of those and copying it over really isn't an option.

Adding a 500 GB drive to the volume is the easiest way to do it, since I have the 500GB drive already, and I don't need spare 3 TB drives - assuming doing it this way is even possible.

[P]

Yes you can. Easy way is to BACKUP, then open Disk Utility, select a drive (not a partition), click the tab RAID (yes, I know what you said, but bear with me) and select "Concatenated Disk Set" from the menu RAID-type. Then add a bunch of drives to the list below the options and there you go.

This used to require you to reformat all drives to join them. Since Lion, this might be possible without reformatting, namely by using Core Storage, but I don't know if Disk Utility uses that method now. Give it a try and see what it says.

EDIT: Realized that you want to remove the drive again after. Hm. You could do that by partitioning the small drive first, adding a partition to each big drive in this manner, and then resizing the partitions as required, I suppose.