Install memtester-4.2.1-1.el6.x86_64 and memtest86+-4.10-2.el6.x86_64 (or updated versions).

# memtest-setup
# memtester 500M
# memtester 10G 2

Check output.

Also look at the 'sar' program. Files in /var/log/sa.

Example run:

sar -f /var/log/sa19