More specifically, they need to be "Mac OS Extended" (Journaled is OK too but largely unnecessary). "Mac OS Extended" is Apple's name for HFS+. The significant feature of this format is that it can support files over 2GBs.
Highlight the drives in question and choose "Get Info" from the File menu (Command+i is the keyboard shortcut). There you can see the format of the drive.
If it needs to be reformatted, move any essential files to another drive and use Disk Utility (YourMacHD > Applications > Utilities > Disk Utility) to reformat.