Very slow Ubuntu Server installation & run on some nodes but not others

Question

We recently bought & self-assembled 7 identical dual LGA1366-based servers. All POST fine, but when I attempt to install Ubuntu Server 11.10 on them, 5 install perfectly. For the other 2, they install MUCH more slowly (e.g. 4-6 hours vs 15 minutes on the other 5 nodes) and upon reboot also are extremely sluggish.

Temperatures are comparable to the other 5 nodes, all RAM is recognized fine. I've tried swapping out hard drives and RAM, and even returned the motherboards for a replacement, but to no avail. I'm out of ideas as to what the problem might be -- any suggestions would be greatly appreciated. Thanks!

Answer 1

Benchmark them with a bootable distribution. Memtest, hard drive stress (linear and random reads and writes), cpu tests... run every sub-system through its paces one at a time in an attempt to figure out the fault point.

Answer 2

Bad disks, controllers or cables? swapping disks and cables around is a fairly inexpensive test. You could also boot the "slow" machines with a LiveCD to see if it suffers even without utilizing the hard disks. (or barely)