NOTE: The most up-to-date steps are available in the following Guide entry: http://guides.macrumors.com/Using_Remote_File_Access_to_Save_Disk_Space_on_Your_MacBook_Air. Please feel free to post your questions and comments in this thread. As we all know, the MBA has a relatively small hard drive. For me, this started to become a bit of a problem when I copied all 35 GB of my music from my main mac pro to my MBA... and suddenly I found myself with a scant 5 GB of free disk space. Not exactly optimal... especially since my Mac Pro has gobs of free disk space just sitting there waiting to be used. So, in my never-ending quest to have universal access to all of my information, the question occurred to me: How can I leave my files on my Mac Pro, but still be able to get to them from my MBA? On Your Home Network When you're at home, on the same network, this is easy: You simply set up File Sharing on your server and then create a connection to it from your MBA. Once you've done that, you can do things like change the iTunes Music folder location in iTunes on your MBA so that it points to the music files on the server, and then use Add To Library to add the music files, which reside on the server, into iTunes. What you end up with is the iTunes Music Library.xml and iTunes Library files on your MBA (a combined 21 MB in my case), but the music files stay on the server (35 GB). So I've saved myself 35 GB of disk space on my MBA. The same trick can obviously be used for documents, photos, etc. The bigger the files you can keep on the server and off the MBA, the better! You just need to make sure that your MBA and your server can talk to each other, preferably via WiFi, and make sure that your files on the server are easily found (don't bury them too deep in folder structures, basically). Away from Your Home Network (Secure) When you leave your home, though, things get trickier. How can your MBA talk to your server if you're not on the same network? Well, one option is Back To My Mac (BTMM), one of the features in the current release of .Mac. It purports to be an easy way for your two Macs to talk to each other... but I did some experimenting with it last night and today, and I can tell you that it's not as easy as they say to set up. Beyond the fact that you have to pay $100 a year for a .Mac subscription, the biggest issue is that your network routers at both ends (i.e., where your server is and where your MBA is) both have to support UPnP (Universal Plug and Play) or NAT-PMP... and they must be correctly configured to allow you to use one of those two technologies. Find yourself in a hotel or a public WiFi spot where neither of those protocols is in use or where they're using an unsupported router, and your BTMM is suddenly worthless. (Apple won't volunteer this information as plainly as I have stated it here. As far as they are concerned, everyone has UPnP/NAT-PMP routers.) Since using BTMM is clearly a hassle, I did a little poking around and found an even better solution which only requires changes on your home router. Basically, if you open a specific port on your router and forward that port to your Mac Pro server, you can get to the server from anywhere you can access the Internet with your MBA. I can't tell you exact steps for your particular router, but here are the basics: 1. On your router, configure port 548 to point to the internal IP address of your Mac server (a Mac Pro, iMac, Mac mini, or some other Mac that's always home and on) for both TCP and UDP. For example, your Mac server might have an IP address like 192.168.1.1. 2. On your Mac server, go into System Preferences > Sharing and make sure that File Sharing is turned ON. Also, click Options under File Sharing, and make sure that "Share files and folders using AFP" is turned ON, and make sure the list of Users includes YOUR account with Read & Write access. IMPORTANT!: You also need to set the access for "Everyone" to "No Access". If you fail to do this, someone might potentially be able to access your server's files simply by directing their Mac to connect to yours. The only account(s) that should be permitted access are "name" accounts (your name and other accounts you specifically created). 3. You will need to know your home network's external IP address: This is the IP address that's assigned to your home by your cable company or ISP. You can usually get this IP address from your router's control panel, or by going to http://checkip.dyndns.com/. (Before you ask: Your external IP address does NOT start with "192.168". It will be something totally different.) NOTE: You could also install a Dynamic DNS client on your Mac and use it to associate a domain name like "www.myhomedomain.com" to your external IP address. This costs a little, but it eliminates the need for you to have to fiddle with IP addresses, especially if they ever change. You can get a Dynamic DNS client here: http://www.dyndns.com/support/clients/mac.html That's all you have to do at home. When you're on the road, you can connect your MBA to your home Mac server using these steps: 4. In the Finder, click Go > Connect To Server. 5. In the Server Address box, type your home system's external IP address. For example, "126.96.36.199". Or, if you have a domain name that points to your home system, you can type that: "www.myhomedomain.com", for example. 6. Click Connect. A password prompt dialog box will appear and ask you for your name and password. Select "Registered User", and then enter your user name and password from your Mac server. If you want, you can check the box for "Remember this password in my keychain". 7. Click Connect. Now you'll get a list of all of the shares on your Mac server. 8. Select the share(s) you want to connect to, and click OK. Voilà! You are now connected to your home Mac server from your MBA. You can access files, copy files back and forth between your MBA and your server, delete files, whatever you want, as long as your MBA remains network-connected. The next time you go to connect, it should go even more quickly (especially if you save your password in your keychain, and if you add your home IP address/domain name to your list of Favorite Servers in the Connect dialog box). Away from Your Home Network (Even More Secure) -- Added 3/3/2008 I didn't post this info earlier, because I wasn't sure it would work... but this weekend I was able to confirm that it does. There are two differences between this method and the Secure method shown above: 1. On your router, configure a port number that you choose (for example, 5678 -- I recommend using a high port number to prevent conflicts) to forward to port 548 of the internal IP address of your Mac server (a Mac Pro, iMac, Mac mini, or some other Mac that's always home and on) for both TCP and UDP. For example, your Mac server might have an IP address like 192.168.1.1. 5. In the Server Address box, type your home system's external IP address, plus a colon and the port number you specified in step 1. For example, "188.8.131.52:5678". Or, if you have a domain name that points to your home system, you can type that, plus a colon and the port number you specified in step 1: "www.myhomedomain.com:5678", for example. Setting your router to perform port forwarding in this manner, rather than just relying on the home server's login security, provides an additional layer of security that will prevent unauthorized users from accessing your home server: Not only would they have to know your user name and password from your home server, but they would also have to know what port number to use, not just the default 548 port number. If they can't even guess the right port number, they don't even get a chance to try your user name and password. Once You've Set Everything Up Once the connection is established, it will also work for programs like iTunes. As I type this, my MBA is connected to a neighbor's open WiFi network (so it's "away from home"), connected through that to my Mac Pro server through the Internet. I'm using iTunes on the MBA to play a copy of a-ha's Take On Me which is stored on my Mac Pro server. I can access my entire music collection in this manner. (The only downside of doing this is that file transfers are limited by network speed. So when I go to another song, it takes a few seconds to transfer the bytes to iTunes on my MBA before the song actually plays. Network hiccups can also be a bother. But at least I can get to the files!) Those of you who have MBAs and who have a little expertise shouldn't have any trouble following the above steps. Hope you enjoy them, and as always your feedback is welcome!