can you perform a disk defrag on the mac pro 2008?

You perform defrag on the HDD.

Use iDefrag, link below.

If you don't have the money for iDefrag, use an ext. HDD, like this....

-- Open Disk Utility.

-- Select the "Restore" tab.

-- Drag the internal startup disk volume to "Source".

-- Drag the ext. HDD volume to "Destination".

-- Click "Restore".

-- Wait a long time.

-- When it is done, quit Disk Utility.

-- Restart holding option key for 45 seconds.

-- Select the ext. HDD, press Return.

-- It will take a bit longer to boot to a Firewire HD, and quite a bit longer to boot to a USB HDD.

-- Open Disk Utility.

-- Reverse the restore process.

-- Quit Disk Utility, and restart.

You should also consider if you need to defrag. With Windows XP or earlier, disk fragmentation put a huge hit on performance. With any version of Mac OS, there is no performance hit related to disk fragmentation. This is well-known to all of us long-term Mac users. The only exception is for huge video file rendering in Final Cut Pro. For that, most pro video editors use at least two external HDDs for just the video, so the OS is on the internal HDD and is not affected at all.