Measuring sequential disk performance with linux is easy - most distros (like ubuntu) come with a tool called hdparm, that is mainly used for tuning and optimizing hard disk parameters, but luckily it also includes simple benchmark functionality - for example the following command
sudo hdparm -t /dev/sda
gives me the following output:
Timing buffered disk reads: 176 MB in 3.01 seconds = 58.55 MB/sec
Of course you need to substitute
/dev/sda with the name of your raw disk device (for example, it might be
/dev/hda for non-SATA disks). Its impossible to get higher transfer rates that that from your disk. Hdparm reads at the very start of the disk for these tests (which is the fastest area of the whole harddisk) and using optimal access pattern.
If you'd like to test your harddisk's cached performance too, you can do so by using "hdparm -tT" (note additional T) to get an output similar to the following:
Timing cached reads: 1198 MB in 2.00 seconds = 598.98 MB/sec
Timing buffered disk reads: 170 MB in 3.00 seconds = 56.65 MB/sec
Of course all of the above tests need to be conducted at least 2-3 times and the results averaged to get some meaningful results..
BTW to check whether your system supports SATA-1 or -2, the following switch is needed:
hdparm -I /dev/sda | grep SATA
which gives as output either one or both of the following lines:
* SATA-I signaling speed (1.5Gb/s)
* SATA-II signaling speed (3.0Gb/s)
Have fun testing.