I have a PC with a single 6Gb/s SATA port, I have a 7200RPM HDD that is my primary drive (i.e. the OS is installed on it), I also have an SSD (450MB/s Sequential R/W, 85K Random Read, 55k Random Write) that is going to be used as a Data drive for my visual studio projects.

Which is more beneficial to be plugged into the 6Gb/s port? Will I notice significant OS slowdown running the HDD (with OS) from another port vs the 6Gb where it was originally?

Both are SATA 3 (6Gb/s) capable drives.

  • I assume both devices are actually SATA III devices? – Ramhound Dec 16 '13 at 14:46
  • I think so. One is a Seagate 7200.12, the other is a Kingston SSDNow v300 – Obsidian Phoenix Dec 16 '13 at 14:49
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    Feel free to confirm by researching both products and finding the product specifications on the Seagate and Kingston website. People have ran operating systems on much slower then 3GB ports for years. Its unlikely you could even match out the transfer rates on either device. Your SSD performance will drop by about 50% on the SATA II port, what you should determine is if, that performance decrease is something you can accept. – Ramhound Dec 16 '13 at 15:14
  • Yeah, both definitely appear to be SATA 3 according to the specs. I'm installing this to drop Visual Studio build time from 20-30 minutes, so I would probably prefer to have the SSD as faster. It sounds like I won't notice too big a difference having the HDD on a slower port. – Obsidian Phoenix Dec 16 '13 at 15:21

Most spinning hard drives for a long time now have a small RAM buffer holding the contents of recently accessed blocks. This traffic likely is able to saturate any link, including SATA III.

But unless you are running programs that only access the same tiny (8MB, 16MB, etc.) amount of data over and over, with only occasional writes, it really doesn't matter. Traffic coming in off the platter will not even get close to SATA II's limits (these days it's approaching SATA I's limits.)

From Wikipedia:

As of 2010, a typical 7,200-rpm desktop HDD has a sustained "disk-to-buffer" data transfer rate up to 1,030 Mbits/sec.[93]

Divide that by 8 to get MBytes/sec and you get about 125MBytes/sec. Older drives and 5400 rpm drives transfer slower.

And given these SATA transfer rates:

6Gbits/sec (SATA III) = 600MBytes/sec

3Gbits/sec (SATA II) = 300MBytes/sec

So, to take advantage of your SSD's 450MBytes/sec sequential read and write speed, you need to put it on the SATA III port.

  • Thanks. I thought that would be the case, but I'm no expert on the Hardware, so wanted to be sure I wouldn't have any major issues with the OS on an HHD on a slower port. – Obsidian Phoenix Dec 16 '13 at 15:28

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