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So I've had my Mac Pro since 2008. I currently have OS 10.6.8 on it. In the last week, it has restarted itself twice while I was in the other room. Since I wasn't there, I don't know if there were any messages. This has never happened before.

When this happens, it takes quite a few hours before it will operate normally without grinding the hard disk for a minute or more at a time. Most applications freeze or become very unresponsive while it does this.

The disk is a 320 GB drive, and there are 42 GB free still. I've done a DiskUtility Verify Disk on it, and it says everything looks normal.

Is this some issue that has a common cause, or do I need to take it in to the shop?

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Although it's unusual for a drive with issues to pass verification, it can happen especially if the failure is one where the drive can retry an operation repetitively and eventually get you your data. Better safe than sorry, keep your data backed up constantly until you resolve this. – bmike Apr 1 '12 at 1:15
Yup, backing up to a 2-drive raid, with periodic drive swaps to keep one offsite. :) – Almo Apr 1 '12 at 1:40

Grinding is a hard drive's way to remind you to be really protective of your drive containing the most up to date backup of your data.

Here is a fabulous app that educates you on what each failure mode might sound like.

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Thanks, will take a look at that. – Almo Apr 1 '12 at 1:41
up vote 0 down vote accepted

The restarts were only when waking from sleep; must have been from network access waking or something. Adding RAM to it fixed the problem. I'm at 4GB now, and it's working fine.

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