6th Generation Airport Extreme Freezing During Time Machine Backups using LaCie 1TB Hard Drive

Question

I recently upgraded from a 4th generation Airport Extreme (short, dual band n) to a new 6th generation Airport Extreme (tall, dual-band ac) in the hopes of having quicker backups and better WiFi performance (I also just got a 13" retina MacBook Pro).
The upgrade has gone poorly, to say the least. Initially, I set up the new Airport Extreme as I had for the old one. Then I plugged in the same hard drive I was using (a LaCie 1 TB d2 Quadra USB2 drive that I bought in June of 2009). I decided to setup my wife's Time Machine backup first (she has a 2010 MacBook Air). I removed the "old" disk (the one associated with the old base station) from her Time Machine configuration, and set up her Time Machine configuration to backup to the same disk on the new Airport Extreme. I was pleasantly surprised to find that it picked up her existing Time Machine backup and incrementally synchronized to it (the backup size was about 300 MB). A few days later, she warned me that Time Machine told her that backups were not working. When I went to look, it was indeed failing.
I tried a few things that didn't work, and I suspected that maybe the backup "transfer" hadn't gone so smoothly as it seemed, so I decided to erase the drive using Disk Utility and start the backup over again. To my disappointment, I found that the backup got about 200MB-1.5GB into the backup and "froze." I left it overnight, and it was at exactly the same place the next morning. The light on the disk connected to the Airport Extreme flashed constantly all the time, and I could hear it spinning, but nothing happened at all.
When I tried to stop the backup, it took a very long time. In the logs, I would see a message like this (this log is from my machine, not my wife's, but it looks the same):
11/19/13 9:40:59.276 PM com.apple.backupd[93334]: Forcing deep traversal on source: "***-mpbr" (device: /dev/disk0s2 mount: '/' fsUUID: 7356274E-D28F-3BC0-9CA8-7F1AA21830B4 eventDBUUID: 99941F9A-AD5F-4FAF-94D2-701C94CA9581)
11/19/13 9:41:57.609 PM com.apple.backupd[93334]: Total content size: 148.2 GB excluded items size: 17.16 GB for volume ***-mpbr
11/19/13 9:41:57.610 PM com.apple.backupd[93334]: Found 674166 files (131.05 GB) needing backup
11/19/13 9:41:57.611 PM com.apple.backupd[93334]: 152.52 GB required (including padding), 498.67 GB available
11/19/13 9:41:57.625 PM com.apple.backupd[93334]: Waiting for index to be ready (100)
11/19/13 9:59:22.407 PM UserEventAgent[11]: com.apple.backupd-auto launchd job disabled
11/19/13 10:00:15.103 PM com.apple.backupd[93334]: Cancellation timed out - exiting
Looking at the Airport Extreme in Finder, I saw that it got stuck, either "Connected as" me, or "Connecting...". The Airport Extreme wouldn't respond to the "Disconnect" or "Connect As..." buttons (depending on the context), and the eject button for the Airport Extreme itself in the sidebar was also unresponsive. Eventually, after 2+ minutes, I got a dialog saying "Couldn't connect to [my base station name]" with instructions to "check its IP" and contact my system administrator if the problem persists. During this time, Finder can seem frozen and unstable.
Through all of the above, the hard disk kept spinning and the light flashed constantly. The drive was warm to the touch in the morning.
I also found that when all this happened, I was unable to connect to the Airport device using Airport Utility. I I couldn't administer it, but the Internet continued to work for all connected devices. Unplugging the disk and plugging it back in worked immediately to bring the system back to a working state. I didn;t even have to power-cycle or reset the Airport Extreme.
I tried a number of things to correct this behavior:
Disabled Time Machine, removed disk, restarted machine, reconfigured Time Machine, and retried.
Tried backup on my 13" Retina MacBook Pro and my wife's MacBook Air.
I actually tried with TWO new 6th Generation Airport Extremes. The first one was a refurbished one. I returned it to Apple and purchased a brand new one. Both of them exhibited the behavior I described above.
Workaround:
Finally, I switched the drive out for a spare that I have (an older Western Digital MyBook and used it for a backup. This drive "Just worked."
So, I have switched to that for backup for now, and re-purposed the LaCie as a drive that I use for making periodic images of my hard drive using SuperDuper. The drive seems to work perfectly (and worked perfectly for several years with older Airport Extreme base stations), so I can only assume there's a bug in the USB driver of the current 6th-generation Airport Extreme.
I hope this helps someone else who's as confused as I was. If anyone has had a similar experience, I would very much like to read about it. I will be reporting this problem to apple right after I post this topic. Please do the same if you experience this issue.

Answer 1

As Bob says, backing-up that way isn't supported.
It's also unreliable. It may work for a while, but this forum, and the Time Machine forums, have many, many posts like this:
*"I've been backing-up via an Airport Extreme for* <some number of days, weeks, or months> *and all of a sudden my backups are corrupted beyond repair."*
In my case, it's happened about 4 times in a year. And that's with a desktop Mac, about 12 feet from the Airport, with the exact same hardware in exactly the same place and no interference.
It is very convenient, especially with laptops. If you want to take the risk, see [Using Time Machine with an Airport Extreme Air Disk|http://web.me.com/pondini/Time_Machine/Airport.html] (or use the link in *User Tips* at the top of this forum).
But do yourself a LARGE favor and take the prominent advice to keep secondary backups, and update them frequently. Sooner or later, you're probably going to need them.