Leopard's Time Machine corrupts Entourage 2008 database backups
When I installed Leopard, I decided that since Apple had embedded an incremental backup solution into the OS, that this would make it more likely that I could keep my backups current. I'm not really good at remembering to take the time to back up my notebook normally, and this seemed like it would be a great solution.
In evaluating this, I read several articles that claimed that using Time Machine with the Office 2008 identity database was suboptimal because it would take a lot of backup space, since the large database file would be completely backed up each hour. This didn't bother me much, because my mail database is so critical to how I work that I would trade a lot of backup disk capacity for a guarantee of losing no more than an hour of e-mail updates due to a hard disk failure or other issue.
Then it happened. I had sync problems after upgrading to 10.5.2 (see my other post on this topic), and in the process of trying to resolve them, I accidentally destroyed all of my calendar data. I figured this wouldn't be a problem; I could just restore the identity folder from my Time Machine backup and I'd be OK. After doing the restore, Entourage would not start because the database file was corrupt. I tried to rebuild the database using the Microsoft database utility. After running for ~18 hours, it failed with an unrecoverable error.
That's when I started to look at the database file in each of the last several Time Machine backups. There were four consecutive hourly backups between 10am and 2pm in which the database file was the same size and had the same last modified timestamp. Since I'd sent and filed numerous messages during that time, it seemed to indicate a problem. I tried restoring each of these backups, and all were corrupt. I then went further backward to the first backup that had a different last modified timestamp on the database file. It too was corrupt. Again there were several hourly backups with this same last modified timestamp, although there should have been modified data between each backup.
I then gave up and called Microsoft. While I was on the phone with them, I found this KB article that states "If Time Machine starts an automatic backup while Entourage 2008 is modifying the user database, the backup process may damage the backup copy of the user database.". The Microsoft support rep I talked to on the phone was more blunt; she said that it was unlikely that any of my time machine backups of the database would be whole & usable, and none would be recoverable via the database utility due to the nature of the corruption.
After close to two days using Outlook via Parallels while I tried to figure out a way to get a relatively recent backup restored, I gave up and went back to the last SuperDuper backup I had before I started using Time Machine. I lost months of e-mail because of this problem, and I'm not at all happy. It seems highly unlikely to me that Apple and Microsoft would not have found this during any reasonable testing. If they had, there should at least have been documentation of the problem, and more likely they should have flagged the Office identify file to be skipped by Time Machine, with a clear notice to this effect in both the Leopard installer and the Office 2008 installer.