There are a couple useful utilities on Linux to test disk input/ouput.
Sequential Disk Access: hdparm
The hdparm command will test sequential disk access and can be used with the below command. Replace /dev/sda1 with the mounted disk you would like to test such as /dev/hda1.
hdparm -t /dev/sda1
The results will output similar to the below..pgpass, disk, hard disk, hda1, hdparm, input, iostat, output, random, reads, sda1, seeker, sequential, sysstat, writes