time machine with an external usb drive on an airport extreme

aah, using time machine with an external usb hard drive connected to an airport extreme.
this is something that is not officially supported by apple. from what i understand, when they were originally working on time machine, it was supposed to be an option. but they pulled all references to it when they released the final version into the wild back in early 2008 or whenever. that said, a lot of people do it anyway. because, hey, it’s a lot cheaper to buy an external usb drive and hook it up to the airport extreme you already own. i had this working in the past, but as you may recall a week or two ago i bought a new, larger external usb drive. since then i hadn’t been able to get the new drive to ever show up as a choice for time machine. there are a lot of people talking about how to make this work, and there are some good help docs floating around the internet. such as…
here’s a blog entry. pay special attention to some of the comments, as they provide good info.
here’s another good how-to guide on the macosxhints forum.
and here’s a time machine troubleshooting guide at discussions.apple.com
doing some google searches will help too. all of these bits of advice might help:

• be sure your drive is in a supported format
• you’ve got “TMShowUnsupportedNetworkVolumes” set to 1 (might or might not need this, depending on how you went about things)
• on the disk, there should be the file: “.com.apple.timemachine.supported”
• mount the drive in finder before looking for it in time machine

the comments in the blog entry above would have helped me, but i didn’t find it until while i was writing this. : ) i had done everything, and the infuriating thing is that it had worked before with my previous (smaller) external usb drive. but nothing i was doing would get time machine to see my new drive. i reformatted, did the two partitions trick, had “unsupported network volumes” set, disconnected and reconnected the drive many times, rebooted the airport extreme, deleted my timemachine.plist file, etc. eventually i went looking in my system.log, and i noticed this entry:
Dec 8 20:12:36 rowboat /Applications/System Preferences.app/Contents/MacOS/System Preferences[798]: Failed to resolve network service using name = F41LUR3\.3XTR3M3 type = _afpovertcp._tcp domain = local.
googling that error provided no help to me, but it made me realize the afp mount probably wasn’t working. i also noted it was escaping the period in my airport’s name (F41LUR3.3XTR3M3) when displaying the name value. i went into safari and tried doing “afp://f41lur3.3xtr3m3.local” and “afp://f41lur3\.3xtr3m3.local” mounts…no good. i went into the airport utility and i noticed whenever you are entering the airport extreme name, it shows you the bonjour (or whatever) name below. it was turning the period into a dash. so i decided to change the name of my extreme from “f41lur3.3xtr3m3” to “3xtr3m3-f41lur3”. i rebooted the airport extreme for the change to take.
i went into safari and tried “afp://3xtr3m3-f41lur3.local” and it worked. i double-clicked on the drive so it was mounted, then went into time machine in system preferences and clicked on choose disk. immediately the usb drive hanging off the airport extreme showed up. i picked it, and it’s now in the process of doing the initial backup.
so here’s the thing to note: time machine does not like periods in the name of the airport extreme. it seems to handle a dash okay though.
p.s. here’s a nice trick to know: that first backup is gonna be pretty hellacious if you’ve got a drive anywhere near modern in size. going over wireless is just plain crazy. but even over an ethernet connection it’s pretty slow. now, a locally-connected drive and an “airdisk” (remote drive, like a time capsule…or a usb drive on an airport extreme) store their time machine backup data in different formats, but once you’ve got the drive set up it’s already ready to go in either local or airdrive style. while doing a local and then converting the drive to airdisk will leave you with worthless local-style backups you can’t use, setting up a drive as an airdisk and then mounting it locally will cause airdisk-style (sparsebundle) backups with local speed. so…set up that airdrive, then when the backup starts, kill it. go into the airport utility, disconnect all users from the shared drive, disconnect it from the extreme and plug it into your computer via usb. go into time machine, hit “choose drive” and choose the now locally mounted external drive. now it backs up over usb (but in airdisk sparsebundle format). when done, unmount the drive and disconnect it from your computer, then hook it back up to the airport extreme. mount the shared drive on your computer, go back into time machine, hit “choose disk” and choose the once-again-airport-based drive. congrats, you just saved yourself a lot of backup time. (don’t get cocky…it’s still gonna take a long time for that first one.)