Is SATA2 bandwidth per port or the entire bus?

SATA2 bandwidth = 384 MB/s theoretical.

If I were to use two SSDs with sufficient speeds in a RAID0 configuration on my P45 motherboard (ICH10R), could the array operate at speeds in excess of 384 MB/s because it's using two ports or would it be limited to 384 MB/s for the array?

It appears that ICH10R has 10 GBi/s worth of bandwidth to play with, does that mean the theoretical top speed of a RAID array on this system would be 1.25 GB/s?

The answers might influence my strategy for any future storage upgrades. 2x 64GB SSD in RAID0 could very well be faster on my system (given the right drives) than 1x 128GB due to not having any SATA3 ports.

I know there's downsides to that sort of configuration, but I'm just theorycrafting in my head atm.

Per port, the controller has a significantly larger link to the rest of the world generally speaking.

On both Intel and AMD boards I couldn't make more than ~1150MB/s using 3 SSD while 2 were making ~1050MB/s max read. After browsing some results on different forums I noticed that 4+ SSD are making also about ~1150MB/s on integrated controllers.
Even that you have 6 SATA3 ports ( like 990FX boards ) it doesn't mean that you can make ~3300MB/s using 6 new SATA3 SSD.
Other thing is that SATA2 bandwidth in theory = ~375MB/s but fastest drives are making up to ~285MB/s. Hard to say how about SATA3 because fastest single drives now can make up to ~560MB/s while max bandwidth in theory is something about ~750MB/s.
P45 boards with ICH10 should make up to 500-550MB/s sequential read using 2 SATA2 or SATA3 SSD in RAID0. I'm not sure if there is any difference between controllers used with P45 and P55 but I was able to make ~750MB/s on Gigabyte P55-USB3 using 3x Crucial M4 in RAID0.

You are overestimating the theoretical bandwidth of SATA.

SATA 6Gbps is 6 000 000 000 b/s.
Converted to bytes this is: 750 000 000 B/s.
Converted to kibibytes this is: 732 422 kiB/.
Converted to mebibytes this is: 715 MiB/s.
Because of 8b/10b encoding you loose 20%: 572 MiB/s.

This is the max possible bandwidth for one SATA 6Gbps port.

Woomack is of course right that the max throughput of the controller depends neither on the SATA port bandwidth nor the bandwidth of the southbridge, but depends on the controllers ability to process the communication.

I'm with you on the bit to byte and byte to kilobyte/megabyte/gigabyte conversions, but this part:

"Because of 8b/10b encoding you loose 20%"

is something new to me. I wasn't aware of that piece of the puzzle.

By this new math, actual SATA2 theoretical transfer speeds would be:

3,000,000,000 * .80 = 2,400,000,000 bits/s divide by 8 = 300,000,000 bytes/s

300,000,000 divide by 1024^2 = 286 MBytes/s theoretical max transfer speeds.

Correct?

Mr Alpha said:

Converted to kibibytes this is: 732 422 kiB/.
Converted to mebibytes this is: 715 MiB/s.

Click to expand...

Is a mebibite expressed as 1 MbB?
This thread was very informative, and indeed, SATA bandwidth is a skinnier straw than most think. Look at the Revodrive 3- to ensure the device achieves 1500MB/s (that's Megabyte not Mebibite) it has a PCIEX4 link.

JeremyCT said:

I'm with you on the bit to byte and byte to kilobyte/megabyte/gigabyte conversions, but this part:

"Because of 8b/10b encoding you loose 20%"

is something new to me. I wasn't aware of that piece of the puzzle.

By this new math, actual SATA2 theoretical transfer speeds would be:

3,000,000,000 * .80 = 2,400,000,000 bits/s divide by 8 = 300,000,000 bytes/s

300,000,000 divide by 1024^2 = 286 MBytes/s theoretical max transfer speeds.

Correct?

Click to expand...

Yes, this is quite correct.

SATA is confusing...