On Networked Backups using Time Machine on MacOSX 10.5.2 [UPDATED]
by moose
I just noticed this after I finally migrated my work MacBook Pro to Leopard.
Previously, when you wanted to backup your computer to a shared drive, Time Machine, instead of simply creating a directory named after your machine and storing all the backup files in it, it would create a sparsebundle named like so: “MachineName_MACaddress.sparsebundle” where the MACaddress bit was the MAC address of the network interface that was used while doing the backup. Here is where it screwed up: let’s says that for the first backup, you choose wisely to do it over gigabit ethernet to speed things up. The sparsebundle is created with your ethernet card’s MAC number in its name. Then you untether your laptop and switch it to Airport. Next time the computer tries to do a Time Machine backup, it WOULDN’T work because it would look for a sparsebundle using your AIRPORT’s MAC address in its name. And if you forced the backup by resetting the drive in the preferences, it would simply create a new sparsebundle named after your Airport’s MAC number and start a new backup FROM SCRATCH. The only workaround was to do your first backup over ethernet, then rename the sparsebundle by replacing the ethernet MAC number with the Airport MAC number. But then next time you connect to your LAN via ethernet, backups would fail.
After migrating my MB Pro to Leopard, I did a first backup using gigabit ethernet (120GB of files), and then I started thinking of ways to allow both wired and wireless backups to work seamlessly. Like creating an alias to the ethernet-created sparsebundle, named using the airport’s MAC number, so as to see if it was just a question of names. So I unplugged my machine form ethernet, switched on Airport and foced Time Machine to recreate a sparsebundle, so that I could copy the file name to paste it as the alias’ filename.
To my surprise, no new sparsebundle was created, because Time Machine picked up the already existing one, and went on updating the backup. Finally, it work as it should.
So now I can have my laptop backed-up all the time, whether I work at my desk and am connected through ethernet or I am slouching on my sofa and surfing via Airport. Good work Apple, keep improving OSX…
[UPDATE] Better than this, not only does it allow you to do your backups over different network interfaces, but I does this: a backup was going on while I was connected via Airport, then I came back to my desk, plugged in the ethernet cable and deactivated Airport. The backup did not stop, it slowed down for a handful of seconds, then continued using the gigabit ethernet connection. Serious magic here!
