7200 rpm 6 Gb/s SATA disk on a 3 Gb/s controller

Question

I have a couple of ST500DM002-1BD142 drives (6 Gb/sec interface) on an IHC10 3 Gb/sec interface AHCI-capable controller. Will there be much of the performance improvement if I will switch these disks to a 6 Gb/sec controller ?

I myself suppose there won't be any, because one Gb/sec is about 120 Megs/sec transfer, so 3 Gb/sec is about 360 Megs/sec. In the same time tests in the internet indicate this drive is capable of ~120 Megs/sec sequential read tops, which is nearly 1 Gbit/sec. All of the rest is for cache transfers, which isn't that effective since it's very small comparing to the drive size.

But then again, if I'm correct in my calculations, why did the vendor bother manufacturing these drives with a 6 Gb/sec interface, why not simply keeping them up with 3 Gb/sec interface, since all controllers do provide lower speeds for backward compatibility ?

Answer 1

You are correct - the speed won't change and the main difference will be that you would get the cache transfer its contents at the SATA III speeds.

Other than that this could be beneficial if you decide to use SATA multipliers on a single port. Basically the multiplier will enable the use of multiple drives to a single SATA port, but limits all drives to the SATA speed (for example 4 drives on a 6Gb/s port will have 1.5Gb/s limit each). This differs from a RAID controller as those controllers enable a full speed potential on each drive while the multiplier limits all drives to the single port's speed.

Hope this helps and feel free to ask any questions you may have! :)