PCIe SATA3 Controllers -- x1 Not Fast Enough?

MrJak · Sep 8, 2014

Okay, I have a PC with SATA 2 connections, and I was looking to boost it to SATA 3, and I found PCIe controllers that used one slot, and others that used 4.

I took a moment and wondered if gen 1 PCIe was fast enough to handle multiple 6Gb/s connections, and found, on wikipedia, that the max, per lane, was as follows, v.1.x: 250MB/s, V2.x: 500MB/s, V3.0: 985 MB/s, and V4.0: 1969 MB/s

So, for my gen1 slot -- an x16, It'd actually be slower than my onboard, right?
Also, if my Gen 2 x16 ever gets freed up, it'd be a bit faster than my on-board, but still not fst enough for two SATA 6Gb, correct?

So why do they make sata3 controllers for Gen1 x1, and gen2 x1, if it's not fast enough, unless I'm wrong about something here? My only idea would be if they hope you won't have anything that maxes out the bandwidth, or for compatibility reasons.

But, as far as the x4 goes, 250MB/s x4=1000MB/s, so just under enough for 2 SATA 6Gb/s, but it'd be perfect for one SSD and two hard drives, (600+200+200)
and Gen2 would be 2000, just 400MB short for maxing out all four Sata 3

(Also, as a side thing, these all support Windows 7, but I have Windows 88 -- they should all still be compatible, right? Especially when the driver itself says Windows 8?)

ddpruitt · Sep 8, 2014

I think you're confusing the definition of x1 and x4. There aren't any SATA controllers that use more than one slot. The x1 and x4 refers to the number of available PCIe lanes. The speed of the lane is determined by the PCIe version. x4 goes 4 times as fast as x1. Unless the specs on the links are wrong the controllers wouldn't be able to transfer 6Gbps (750 MB/s). You would need either more lanes or a higher PCIe version, and you'd have to account for overhead. Once you add these things together things tend to get messy.

On the other hand it would be extremely difficult to saturate even a 250 MBs connection. An SSD would essentially have to transfer something directly to high speed interface to be able to use up the entire bandwidth, HDDs can't even get close. If you're usage pattern is like most people you're SATA 2 connections are fine and I would doubt that you would actually notice a difference by going to full SATA 3 connections on all of your drives.

MrJak · Sep 8, 2014

Well, there are physical x1, x4, x8, and x16, as shown by this image:

And my board has two Gen1 x1, one Gen1 x16 -- the middle one, and two Gen2 x16:

The specs are listed on newegg, plainly: XFX 790i ULTRA SLI

MrJak · Sep 8, 2014

ddpruitt :

Actually, I just now saw that they had blank pins for the X4 -- that is rather peculiar.

Edit: Okay, the x4 is actually two-lanes, so that would put them at 500MB/s on Gen1 PCIe, and 1,000MB/s on Gen2?

Though the X1s don't list how many lanes? I assume one lane?

Also, I know two lanes of Gen2 will be enough for maxing out a Samsung 840 evo 250GB, and give enough room for a 200MB/s Hard drive, assuming both got maxed (they'd max at around 740MB/s read)

Also, the reason I'm worried about both an SSD and a hard drive, is because I am slightly worried that my sata controller would have issues with a 3TB drive, if I knew that wouldn't be the case, I'd only worrry about the SSD getting extra bandwidth.

Though I just found out that I have been misinformed for the speed of sata 2 and 3. They've been stated as 3Gbps, then 300MB/s, and 6Gbps, and 600MB/s, when it's really 375MB/s, and 750MB/s...

ddpruitt · Sep 8, 2014

The x1, x4, x16 refer the the length of the slot, not the number of slots per se. Most PCI devices are designed so that they can use x1 even if they are designed for x16, albeit at a speed reduction. x1 is just a single lane. Some MBs have blanks for unused lanes for support. x4 on PCIe 1 is 1000 MB/s on PCIe 2 is 2000MB/s, again not counting overhead. The size of the drive has zero to do with the speed you need. A 3TB HDD will transfer less peak data than a 256Gb SSD. I would actually measure the type of throughput you're using before considering a controller. You may be better off holding off until you upgrade your system. To max out an SSDs read and write speeds requires special conditions that most people aren't duplicating, and in fact random access tends to be more accurate. I'm sure the controller will connect to SATA 3 devices, they just won't be at SATA 3 speeds, marketing at it's finest I suppose.

MrJak · Sep 8, 2014

ddpruitt :

Okay, by worrying about size, I'm worried it won't detect the full size -- that does happen some times, where 3TB reports less than 1TB in BIOS, and windows, and it's due to a controller issue.

Now, as for the speed, my two SSDs are individually rated for 205 seq Read, and 110 seq Write
In Raid 0 they show this, and I'd be fine with that, but I'd like to switch back to a single drive.

I'm also trying to find a way for someone else to get past the issue of a single 3TB boot drive on a non-uefi board, without using extra partitions.

MrJak · Sep 9, 2014

Okay, found this one that has all four lanes: http://www.newegg.com/Product/Product.aspx?Item=N82E16815124130

That should get me 2,000MB/s on Gen2 Pcie, and enough to fully saturate two Sata III Connections, and still procide enough for better than USB2.0 speeds on the USB3.0, but more realistically, I'd, probably only use half the max bandwidth at most.

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PCIe SATA3 Controllers -- x1 Not Fast Enough?

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