It has always been supported on a TC.. and is now also supported on the latest Airport Extreme.
The drive must be Mac formatted.. this is essential part of how TM works.
I know backing up to an external drive attached to an Airport Extreme is not supported,
It is now..
See the details here.
What was different about a TC and an extreme on the earlier versions was never made clear.
Thanks LaPastenague! Good to know this was always supported on Time Capsule – I suspected as much, since the wording was specific that it wasn't supported on the Airport Extreme, but just wanted to make sure.
Great that they've added this to the newest tall Airport Extreme - to corrobate this, I looked at the user Q&A in the Apple Store and some helpful people there referenced the exact place it says this in the new AE manual. Hooray!
Now my choice is whether to buy an old refurbished Time Capsule or a new Airport Extreme.
Let's be sure to stress this caveat from Pondini:
But it's not reliable and not supported by Apple on the older, flat models. They have different hardware. If there's trouble with it, you won't get much, if any, help from Apple.
Yes, I know this all too well - my current setup is an old (flat) Airport Extreme with an external drive, and my backups get corrupted constantly. I always figured it was OK since they were just backups, but its become too much of a hassle to start over every month or so.