One of the biggest purposes of NCQ

[d3m0n1q_733rz]

Hey guys! How many of you knew that it's possible to connect more than just one drive to any given SATA port?
Que the
It's true! And I'm here to tell you how to and why it works. Upon booting, each HDD is given a specific address by the computer. Unlike SCSI devices, these addresses don't need to be manually set.
"Well then, how do I connect more than one of these buggers into my SATA port and free some ports?" It's easy! Use a SATA port multiplier. By connecting your port multiplier to your board and your 2 or more drives to your multiplier, your port multiplier can intelligently "direct" traffic based on the device indicated by your NCQ tag. And the best part? Your computer will see your drives the same as always and they can be included in your RAID arrays. No more wasted bandwidth on your 3 or 6 GB/s SATA ports and blazing speed.

[baius]

d3m0n1q_733rz, your OP suggests that you have tried Port Multiplication with success.

Is this true?

I'm fairly sure I've decided against using this method, because my reading of various forms suggest that SATA-based PM is too unreliable, there isn't a consistent standard amongst manufacturers, 'hard drives going missing when system is idle', etc.

So I'm sorry: I think I just poisoned my own question.

Anyway, if possible, please share your experience.

EDIT: Also, I just remembered. The hardware to enable PM seems inordinately expensive compared to a RAID card. A 1-to-5 'splitter' seems very expensive. £50 for 4 extra ports => £100 for 8.

If, and this is a fairly big if but... if one has a spare PCIe x4/x8/x16 slot, then surely a RAID card like the HPT 2720sgl would be better value, and possibly more stable.

The AddOn cards also worry me that they have 'Raid Options' - it seems to over complicate the simple task of daisy-chaining a SATA port.

[d3m0n1q_733rz]

I would say that the expense is most likely due to the fact that hardly anyone knows about them. I could go to a computer store like MicroCenter and ask if they have SATA port multipliers and they take me to PCI cards because they don't know what a port multiplier is.
It comes down to supply and demand. Because nobody knows what they are, few places have made them. But the addon cards don't have RAID options if they're true port multipliers. They should be no different from a USB hub. Real port multipliers don't have PCI connections. Here's an example: http://www.addonics.com/products/ad5sarpm-e.php
Oh, and here's some specifications: http://www.serialata.org/documents/pm_100_Gold.pdf

[Agent]

They mostly solve a problem which doesn't exist though. Rarely do people run out of SATA ports on a modern system and if they do, buying a addon card is cheap and less hassle.

[Funkstar]

Here's an example: http://www.addonics.com/products/ad5sarpm-e.php

As I understand it, the main use of port multipliers like that is so you can have however many SATA drive in an external case and just a single eSATA cable connecting them to the host system. They then appear to the OS in exactly the same way as if they were in the main PC case.

Now, the grown up version of this is to go with SAS multipliers. These can be used with hardware RAID cards and can let you have RAID arrays of perhaps 16, 20 or 24 drives. Or multiple smaller RAID volumes on the same card. These cards are expensive and rare, but they work well in the right situation. Again these are often aimed at having your disk array in a separate enclosure to the host system (perhaps a U1 server and a U4 or U5 disk bank). I thought about getting one to pair with a PERC 6i at one point, but apparently they only work with the PERC 6e because of firmware limitations of the Dell controller.

[shaithis]

Agreed on the price aspect.....I really cannot see how they are in any way financially viable for end users. I have looked at them a few times and have each timed scratched my head at their cost.

[Funkstar]

For regular consumers, no, they are not the answer. But they do serve a purpose and if you have that particular problem, they seem to solve it fairly well.

Here's another usage case for SATA multipliers, although these days it is a very rare occurrence. It lets you attach a cage full of CD/DVD/BD writers to a single system with a single cable. You could connect 4 or 5 writers to a laptop with a single eSATA cable. In the past you would have used SCSI, but that isn't an option these days, and USB can be a bit flakey and is a bit limited bandwidth wise unless you are using USB3.

Not a common thing to do, but if you need to do it, these things are a reasonable amount of money to solve your problem.