Mac Disk util did repair my volume header error but why....

Question

I was wondering what might have caused the Volume header error that I just had to repair? Macheine was never downed... good power.. I am perplexed.

Answer 1

If it happens once in a while, then it's most likely something "glitched" in the memory. Even good memory can have a bad nanosecond occasionally.
If it starts happening fairly often then it's usually either bad memory or bad blocks on the hard drive.
There are third party memory tests and hard drive tests you can purchase or download that will check these things out. What I usually recommend as a starting point for memory tests, though, is the Apple Hardware Test (AHT) that came with your computer.
For your Mac Pro, I believe it is on the first install disk, Here's how you would run it:
1. Insert install disk 1 into the computer and then shut down the computer.
2. Once the computer is shut down, start it up and immediately press and hold down the D key. Don't let go until you see the AHT logo.
3. Eventually you'll get to a screen with a Test button. Before clicking it put a check mark beside Run Extended Test. This could take quite awhile, especially if you have lots of RAM (the memory test takes the longest). And expect the screen to go all sorts of colors and stuff when it tests the video RAM.
4. If there are error messages then write them down and call Applecare because it's guaranteed they'll say it needs a repair of some sort.
If there are no error messages it's not a guarantee there's no hardware problem. If it's an intermittent memory issue, the AHT may not catch it. In that case I recommend running it overnight in "looping mode". This will run the tests over and over and over until you stop it (using Ctrl-C I think) or until it comes up with an error message. To turn on looping mode follow the instructions above but before you click the Test button press Command-L.
Once again, if there are error messages call Applecare.
For the hard drive, one thing you can do if you suspect bad blocks (and this is a pain) is to back up all your data and then zero out your hard drive and then reinstall OS X. This will erase everything on the hard drive which is why you want to back up your data first.
Essentially what that does is writes zeros across the whole hard drive. If it finds a bad block then it marks it as bad and the computer won't store data in that block anymore. A few bad blocks isn't going to take up much space. Blocks are usually measured in KB so it takes a lot to equal even a GB.
For the hard drive, it's usually best to find software that can scan and test the blocks without erasing anything, though.