How does SATA port multiplication work?

Question

After reading this blog post on cheap storage, I'm curious about how SATA port multiplication works.

• Does multiplication require something special on the host machine (i.e. can any SATA port be multiplied)? If so, what spec should be checked for?

• Can you daisy-chain multipliers for even more ports?

• Does multiplication impact performance? I thought the one-channel-one-drive configuration is one of the reasons SATA is faster than most other interfaces.

Answer 1

According to this article on tom's hardware:

• The spec allows a maximum of 15 devices per SATA connection
• The SATA controller and the port multiplier have to play nice together, which is not a given and usually works only with dedicated SATA controllers. The post you linked to also says that the onboard controller didn't work well with the port multipliers.
• No daisy-chaining - the port multiplier does not dupe the controller into believing it's only one drive.
• Of course it impacts performance: the drives have to share the connection's bandwidth. If you hook up 10 drives via a 300MB/s SATA 2.0 connection, that leaves only about 30 MB/s to each drives, which is about a third of what a modern drive could supply. Of course that is only relevant when the drives are actually all doing sequential reads at the same time.

Answer 2

I would also suggest, when using port multiplication, buying the eSata controller with the eSata enclosure. I've noticed that some enclosures are very unstable with some controllers. Also if you mix both 1.5Gbps and 3.0Gbps drives in the same enclosure, it might be advisable to force the eSata speed to 1.5Gbps.