Hello John, see how many of these you can answer...
See if the Disk is issuing any S.M.A.R.T errors in Disk Utility...
Says "SMART Status: not supported"
Open Activity Monitor in Applications>Utilities, select All Processes & sort on CPU%, any indications there?
I'm not sure how to read all this- but the CPU shows only about 50% usage most of the time.
How much RAM & free Disk space do you have also, click on the Memory & Disk Usage Tabs.
RAM Used: 1.14 out of 1.25 GB
Free: 133 MB
Wired: 170 MB
Active: 660 MB
Inactive: 316 MB
Shows Virtual Memory pretty consistent at 585 MB
Console in Utilities & see if there are any clues or repeating messages when this is happening.
Nothing noticeably repetitive.
In the Memory tab of Activity Monitor, are there a lot of Pageouts?
I see nothing referred to as a "pageout" in the list.
Other possibly relevant information:
Disk being copied from has 358 GB used, 107 available
Disk being copied to was formatted prior to starting the copy (Mac Extended Journaled formatting).