What possible use is a PCI-E x1 SATA III controller?

[WyomingKnott]

I keep seeing SATA III controllers that have a PCI-E x1 connection. Someone help me out with my math.

SATA III: 600 MB/sec
2 SATA III ports on the card: 1,200 MB/sec
PCI-E 2.0 x1: 500 MB/sec

So what use is a controller with a built-in bottleneck?

 

[Chainzsaw]

Well the only reason (if i did this) for me to get a PCIE X1 Sata III controller would just be for extra storage...I wouldnt even bother putting a Sata III SSD on them - just a mechanical HDD.

Besides that your right - it would be a huge bottleneck with an PCIE X1 connection.

 

[sminlal]

You're going to see a lot more SATA-III controllers because the chipset manufacturers have moved to that standard and aren't making the SATA-II chipsets any more. They don't need to because SATA-III is backward-compatible with SATA-II.

But some people will still have the need to add ports to their systems, and they may not have an X4 slot to use. It's perfectly crumulent to plug a dual SATA-III port card into a PCIe X1 slot if all you're planning to attach to it are hard drives. The transfer rate of hard drives isn't fast enough to saturate the connection anyway.

You probably wouldn't want to plug a couple of SSDs into it, but even if you did it would still work, and you'd still get the major benefit of the SSD - faster access times.

 

[WyomingKnott]

How to pick a best answer; you are both right.

It's the same answer I give people who ask why there's an SATA III port on an HDD, when the HDD can't saturate SATA II. OTOH, my choice of motherboard was dictated by the availability of an x4 slot for my UltraSCSI card, now retired.

 

[WyomingKnott]

Best answer selected by WyomingKnott.

 

[igbayirdbay]

I keep seeing SATA III controllers that have a PCI-E x1 connection. Someone help me out with my math.

SATA III: 600 MB/sec
2 SATA III ports on the card: 1,200 MB/sec
PCI-E 2.0 x1: 500 MB/sec

So what use is a controller with a built-in bottleneck?

You have to be creative in which drives you hook up to the two ports. If one is for an optical drive used for playing Blu-ray discs, you want to avoid attaching another device you would use at the same time to the second port of the card. Either drive would enjoy near full speed by itself. If you read from an optical drive and try to write to a HDD on the second port, then you have a bottleneck. If you are simply trying to get more hook-up points for your SATA III hardware, it is still a good, cheap option as long as you plan your drive usage accordingly.

 

[sminlal]

If you read from an optical drive and try to write to a HDD on the second port, then you have a bottleneck.

That sort of thing was a problem with IDE drives because both drives shared the same ribbon cable to the motherboard. That's not true of SATA though - each drive has its own port with its own buffering and protocol support and data can flow slowly to one drive while it flows quickly to another. As WK pointed out there can be a bottleneck if the aggregate data rate of both ports exceeds that of the PCIe connection, but a slow drive on one port won't affect a fast drive on the other.

 

[igbayirdbay]

That sort of thing was a problem with IDE drives because both drives shared the same ribbon cable to the motherboard. That's not true of SATA though - each drive has its own port with its own buffering and protocol support and data can flow slowly to one drive while it flows quickly to another. As WK pointed out there can be a bottleneck if the aggregate data rate of both ports exceeds that of the PCIe connection, but a slow drive on one port won't affect a fast drive on the other.

True enough, but that was not what I was saying. He asked what was the point of having these types of controllers when the total throughput from the two ports was theoretically double what the PCIe single lane port was capable of handling. My response was you can be creative about pairing drives on the card to minimize instances where both drives would be using considerable bandwidth at the same time. If you have 2 optical drives to connect to the 2 ports and do not anticipate using both at the same time, you will never bottleneck the drives at the slot because only 1 will be using the bandwidth at a time. Still, both drives will be hooked up and ready when needed. This gives the 2 port PCIe x1 card value.

 

[sminlal]

True enough, but that was not what I was saying. He asked what was the point of having these types of controllers when the total throughput from the two ports was theoretically double what the PCIe single lane port was capable of handling. My response was you can be creative about pairing drives on the card to minimize instances where both drives would be using considerable bandwidth at the same time.

I can see how your argument would apply if we were talking about SSDs (as indeed we did earlier in the thread). But for optical and HDD devices it really doesn't matter because even two of the very fastest HDD drives still fall way short of being able to saturate a PCIe 1X lane. And of course optical drives are even slower.

It doesn't matter how hard you run the two drives or what combination of optical and/or hard drives they are - anything short of a reasonably fast SSD just isn't going to be bottlenecked by the card.

 

[igbayirdbay]

I can see how your argument would apply if we were talking about SSDs (as indeed we did earlier in the thread). But for optical and HDD devices it really doesn't matter because even two of the very fastest HDD drives still fall way short of being able to saturate a PCIe 1X lane. And of course optical drives are even slower.

It doesn't matter how hard you run the two drives or what combination of optical and/or hard drives they are - anything short of a reasonably fast SSD just isn't going to be bottlenecked by the card.

Bottom line to your point is the same as mine. The SATA III card in the PCI-e 2.0 x1 slot has value. You could use a SATA 2.6 card as long as you don't mind needing to upgrade again as soon as your drive needs change (SSD) or technology provides us with faster HDD's. The price difference between the two cards is not enough to warrant buying a SATA II card instead of a SATA III card. You're the expert here, I was just making an observation the card is not useless.