I just added some external storage to my Mac, and wanted to share the decision and installation process. First, let's start with the choice of type of storage. Basically you have directly connected hard drives (DAS) or network attached boxes (NAS). There are cloud applications, but I just want to address local solutions here.
NAS offers some handy benefits such as huge storage capacity, RAID support, web access and so on. But the network connection and latency will affect the editing process in programs like Lightroom. If you're like me and capture 1000 or more frames on a typical shoot, this can be a problem in your post workflow, particularly if the client has a deadline. I don't take short cuts in editing, so even an extra minute per image is problematic.
Although a little more awkward - a drive plugged into your laptop - even Firewire provides a much faster interconnect for editing than wifi. If you have USB 3.0 support, it's even faster - way faster. What's even better is that they're dirt simple to install, can be changed out when they get full, can be partitioned for multiple uses, and can be configured for RAID if you really feel the need. I added a 1 TB WD My Passport Studio. The instructions are easy to follow and are divided into three areas -- basic install, the Mac Turbo feature, and security utility. Unless you're taking the external drive someplace where others will have access, you can forget about the third, which includes a password you have to enter each time the drive starts. The other two took me about 15 minutes to install. The drive shows up in your Finder window, and is journaled for the MAC OSX, so it's already formatted. There you can give it another name if you like. Probably a good idea if you expect to add more later. Be sure to eject it when you shut down and want to unplug it.
Just make sure you use the "copy" command on Import (middle of the frame on top) and specify your new drive as the destination in the top right corner of the screen. Downloading from my camera card to the drive was just about as fast as to the internal drive, and I noticed no difference in the editing process.
I shoot everything and store everything in RAW, so my files are around 20 MB each. A 1 TB drive can therefore hold about 50,000 images. If you want full RAID 0 protection, get two of them, daisy chain them on the Firewire bus and set them as as a RAID set, using the RAID utility on the MAC. If 1 TB seems too small, these little drives are available in 3 TB capacities today, and probably more soon. But the nice thing is you can just buy more as you need capacity. Just remember a way to know when you changed from one to another, as Lightroom will think they're connect when you bring up a collection.I just use install date, since I date code all my collections, making it easy to know which drive I need to connect to view/edit a collection.
That's it. Let me know how this works for you