Backing up USB-connected drives on an Airport Extreme

I love the fact that my Airport Extreme can serve as a “poor-man’s NAS” by making USB drives available as Samba shares.  But when I wanted to back up one drive to another, I ran into terrible problems.   Here’s how I solved these problems.

I started out with two FAT-formatted drives.  FAT is lame, but I’ve got Windows laptops and a MacBook Pro at the house, so I figured that if I ever needed to directly connect the drives to one of these laptops, FAT would be the most accessible.  My plan was to use one drive as a primary drive and periodically back up to the second drive.  (Hello, software RAID support for the Airport Extreme, Apple?)

I quickly ran into problems with one of the Windows laptops.  It could connect to the drive on the AE, but the connection was not reliable. 

I eventually traced this down to an incompatibility between the wireless chipset on this laptop (a Toshiba Satellite R15 tablet PC) and the AE.  It’s an Intel Pro/Wireless 2200BG chipset.  Some folks have pointed to the Power-Save Polling as the culprit, but I was never able to get the built-in wireless to play nice with the AE.

So I bought a cheapo USB wireless adapter (Rosewill RNX-G1W) for the Toshiba, and things worked like a charm from that point on.

Once I got the primary drive working reliably, I needed to figure out the backup solution.  I originally thought I’d just connect both drives to the AE, mount them both from a client laptop, and do a recursive copy between them.  So naive.

I could not get this to work — the laptop would always end up losing one or both volumes.  Sometimes this would happen a couple of hours into the backup process.

I tried this from the MacBook Pro and from a Windows laptop.  No luck.  Under Windows, I tried using the Explorer, I tried Cygwin, and I even tried a special batch copy client for Windows.  All failed.

So my next approach was to try connecting directly to a laptop and perform the copy.  I tried it with OS X — the drives eventually unmounted during the copy.  Windows also had problems.

In desperation, I reformatted the drives as Mac OS Extended, thinking that maybe the MacBook Pro would handle its native file system format better.  Still, I got the disconnects.

Finally, I thought of another approach: using the old backup standby of tar.

With the primary drive mounted on /Volumes/Primary and the secondary on /Volumes/Secondary, here are the commands I used:

Eureka!  It worked.  No unmounting.  It took a few hours to backup about 100GB.  But it worked.

Gaining confidence, I thought I’d try it over the network with the drives connected to the Airport Extreme.  But this failed with errors like


So it seems the way to get a backup is to disconnect the drives from the AE, connect them directly to an OS X machine, and use the tar commands to recursively copy the filesystem.

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