Ask TUAW: How do I setup a Mac with both an SSD and a regular hard drive?

Reader Mark R. Friedman wrote in to ask about setting up a Mac Pro with an SSD in the second optical drive, keeping the /Users folder on another drive; he wasn't sure how to do it. Macworld just discussed one method, using the built-in home folder path controls in System Preferences. The magic begins with right-clicking or Control-clicking the user name in the Users preference pane, which allows you to access the Advanced Options that control where the home folder lives on your drive.

This was the same approach my friend Jon Deal detailed in an article explaining how to Move Your Home Folder Off Your SSD Boot Drive in OS X way back in November 2009 (because he's a huuuuuge nerd. I kid because I love, Jon) but his information is still relevant. If you want to move your entire /Users/ folder to another drive, or to a different partition on the same physical drive, Jon's instructions will work fine.

There are, of course, other ways to do it.

Matt Legend Gemmell rightly points out that while moving the entire /Users/ folder is straightforward, it may not be your best option. He recommends only moving some specific folders to the non-SSD drive, specifically Downloads, Movies, and Pictures (for some users, Music may also fit in that category). Those folders tend to be the largest ones, and can easily be symbolically linked from your non-SSD drive. (A symlink is the UNIX equivalent of an OS X alias or a Windows file shortcut, but in some edge cases and for some applications it behaves more predictably than an alias would.)

Having used a MacBook Air for about a year now, I can't stand to use a non-SSD drive anymore. Even accessing files on an HDD is slow enough that I want to avoid it whenever possible.

Another option for setting up your new SSD-based Mac

Mark asked for instructions for setting this up on a Mac Pro, which has plenty of drive bays for additional hardware. Laptop users (who ordinarily would not have space for two fixed drives) may be considering replacing the SuperDrive with an SSD. The user folder process is the same for any of them.

Step 0: I'm borrowing this from Jon, but before you do anything else make sure you have a working backup of all of your stuff. Check to make sure. Disconnect any drives which don't need to be connected during the install to reduce the chance of accidentally installing it on the wrong drive.

Step 1: Install Mac OS X directly on your SSD (if it isn't already). With Lion this will mean downloading the Lion Installer from the Mac App Store and following the steps to install it on your SSD.

Step 2: Don't migrate your apps and settings. If you're switching to a completely new drive, now is a good time to make a clean break from cruft you don't really need: apps you installed but never used, leftover project files from 2007 that you'll never look at again, that folder of animated GIFs from Geocities, etc. Start with a clean installation of OS X. Only install apps as you need them.

Step 3: Use your non-SSD as a reference drive. It will appear as /Volumes/{drive name} and you can access your old files as you find you need them.

For the purposes of this article, let's assume that your old drive is /Volumes/OldDrive. You will see a bunch of folders in there, including /Users/ which is where your old home account is located, including your old iTunes and iPhoto libraries, if you use them. Matt Gemmell explained how he linked some folders to their usual spots (if you want to do that and are not comfortable with using Terminal.app, I recommend SymbolicLinker which will make it easier to manage.) One potential tricky part is that OS X does not want you to delete some "default" folders, so it makes it difficult to do so. You can either fight it, or you can just leave the system folders where they are and just tell various apps to look elsewhere for their data.

For example, if you start iPhoto or iTunes while holding down the Option/Alt key, it will ask you where to find their library. If your libraries have gotten out of hand, this is a good time to start over. It is particularly easy in iTunes to put the media (songs, videos, podcasts, etc) on an external drive, but keep the actual library files on your SSD. Having the library files on the SSD will makes iTunes faster than you've ever seen it before (iTunes is still one of my least favorite apps, but at least it's faster).

Most Mac web browsers will default to saving files to ~/Downloads/ but you can change that in preferences to /Volumes/OldDrive/Downloads or anywhere else on the non-SSD drive. The same goes for movie/video files. They don't have to be in ~/Movies, that's just where OS X defaults to putting them.

Which trade-offs do you prefer?

Now you have are three options for using an SSD plus HDD:

1. Move Your Home Folder Off Your SSD Boot Drive in OS X as Jon Deal suggested.
2. Keep everything on your SSD except for a few linked folders as Matt Gemmell suggested.
3. Use the SSD and change applications to point to your HDD as I have suggested by changing preferences where possible.

Each method has its advantages and disadvantages.

Jon's is the easiest, but you lose some of the advantages of the SSD for applications which store library/cache files in your $HOME. This is probably the best solution if you have a small SSD.

Matt's method has you tinkering around with folders Apple really doesn't want you messing with, but it will work with all applications, even ones which don't let you define where their data is kept. If you want to dive in, set everything up, but then not have to worry about changing much after the initial setup, Matt's ideas may work for you. If you have specific applications that you use which cannot change where their files are stored, this is your best option.

My suggestion tries to maximize the SSD benefits for those willing to change some app settings. It works especially well if you've been lugging around a bunch of files that you don't really use that often and are ready for a clean start.

I've done this with a 250 GB SSD, and currently have 168 GB free. My large downloaded files, movies, music, and pictures are all on external drives. I use DiskAlarm (US$2, Mac App Store) to keep an eye on available space on the SSD. When it starts to get low, I go through ~/Downloads and ~/Desktop delete files I no longer want or need, or move them to external storage if I no longer need them. Of course, I am also using a MacBook Air, which means that I don't have the option of a second internal hard drive. If you do, you may want to do things differently.