SSD shootout: PCI Express blows away SATA and M.2 in throughput testing

For the better part of a decade now, the traditional interface for hard drives has been Serial ATA (SATA). With the advent of the solid state drive (SSD), new interfaces have come into play designed to speed up throughput, because the SATA interface has rapidly become the bottleneck in drive speed.

When SATA was first introduced in 2003, its 1.5Gbps of throughput seemed more than adequate for 7,200 RPM drives. The Serial ATA International Organization (SATA-IO), the trade group that collectively developed SATA, has since increased throughput to 3Gbps for SATA II and then 6Gbps for SATA III.

A SATA 3.2 spec, with 16Gbps, was introduced in 2013 but has been slow to gain traction. SATA 3.2 is also known as SATA Express since it supports both the legacy SATA III interface as well as connections to PCI Express lanes on the motherboard.

Out of the SATA 3.1 spec came mSATA, a tiny SSD drive with one or two SSD chips on it, offering a small (under 100GB) amount of storage to netbooks and other low-end devices. MSATA used the PCI Express Mini Card layout and was eventually replaced by M.2 which used a larger form factor – about the size of a stick of gum – to add more chips and thus hold up to 500GB. M.2 is a mechanical form factor, not an interface. The interface of the drive is either PCIe or SATA.

On the enterprise side of things, servers began using PCI Express cards for SSDs to get maximum throughput, since PCI Express offered 7.877 Gbit/s of throughput per lane and PCIe 3.0 slots could have 16 or even 32 lanes, although 16 is more common. That translates to 126Gbps, far exceeding the SATA interface.

So now you have three choices of form factor for an SSD drive – SATA, M.2 and PCI Express -- at three different price points. Is there a difference? That's our mission here. We'll dig in to the three types.

First, the hardware that we used in our testing. Our test PC featured an Intel Core i7-4770 processor, Gigabyte Z97 motherboard, Corsair 2,133Mhz DDR3 memory, PNY GTX670 GPU, Corsair 650 watt power supply, Windows 10 (with one exception) operating system.

The drives that we tested were:

1. OCZ ARC 100 500GB – OCZ's consumer drive ($139.99) - Buy it on Amazon

Part of OCZ's affordable line of SATA drives, this one uses Toshiba 19nm MLC memory and OCZ's Bigfoot 3 controller. Memory is a little slower than the higher-end products and it lacks extra bells and whistles of the Vector. It's quite cheap because it's being discontinued, with new drives coming soon.

2. OCZ Vector 180 500GB – OCZ's power user drive ($149.99) - Buy it on Amazon

Another SATA drive, it uses the same memory chips as the ARC 100 but at a higher clock speed (397MHz, vs 352MHz in the ARC 100) and it has 'Power Failure Management Plus', or PFM+, designed to save data in the event of sudden power loss. It also has full AES-256 encryption, plus support for Microsoft eDrive. Its warranty is five years, vs. three years for the ARC 100.

3. Crucial MX200 M.2 500GB ($189.99)

4. Samsung PCIe SSD SM951 M.2 128GB ($99.99) - Sold on Amazon

These SSDs are about the size of a stick of gum and sit on the motherboard in a slot between the CPU and PCI slots. That eliminates the need for power cables and a SATA cable. Crucial, the brand name for Micron products, comes with a feature called Redundant Array of Independent NAND (RAIN), which protects against data corruption in case of power loss, along with adaptive thermal protection and hardware-based 256-bit AES encryption.

M.2 drives can come in either SATA only or SATA/PCI Express form. If the former is like the Crucial drive I tested, then you have the same interface as the regular drive, you're just spared the headache of snaking power and SATA cables through your PC. This is not a bad thing. But if you want speed, you need the PCIe version. Check the labeling carefully, it will say if the drive is SATA or PCIe.

Not every motherboard has a M.2 slot on it; Z87 chipset motherboards, for example, don't support it. Motherboards from X99 and Z97 forward often do have a M.2 slot on the board. If not, you can buy an inexpensive ($25) PCIe card that you can mount the M.2 drive on and plug it into a PCIe slot and it will work. But remember, the PCIe card only works with a PCIe M.2 drive. It won't support a SATA drive.

One nice feature with the Crucial drive: they give you a free license for Acronis True Image, so you can migrate your old hard drive to the SSD.

5. Intel 750 PCIe SSD 400GB model ($349.99) - Sold on Amazon

Non-Volatile Memory Express (NVMe) is a protocol specifically designed for SSDs using PCI Express. Recognizing the limitations of the SATA interface, a consortium of vendors including Intel, Samsung, Sandisk, Dell, and Seagate got together to take advantage of the much faster PCI Express interface for SSDs. Like the M.2 drive, it's not going to run on anything older than an Intel X99 or Z97 chipset and you need a PCI Express 3.0 slot on the motherboard.

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PCIe cards are also the only drives that will really require you to fiddle with settings in BIOS/UEFI. Intel's documentation in the box isn’t very helpful. I found this (PDF) very thorough and helpful online, including BIOS settings. But that won't do you a lot of good when you are looking at a PC that won't start.

Still, once you get it going, the PCIe card has a much faster I/O pipeline that's only going to get faster and is unique to a PCI Express card. At first, these cards were prohibitively expensive, several times the cost of a SATA drive, but the prices have plunged recently. NewEgg has the 400GB version for $349 and Micro Center was selling it for $269.

6. OCZ Vertex 4 500GB drive - Sold on Amazon

The Vertex is the drive in my personal system. It was considered top of the line just three years ago. I threw it in to see how a drive three years old compares to the latest. I shut down everything, all background apps and unnecessary services, to run the benchmarks, but I will say up front, it's not a perfect comparison since the drive had Windows 7 while all of the test drives had Windows 10, and performance will be inherently different.

The Benchmarks

OK, let's dive into the tests. In every instance, the higher the number the better.

It's not even close. The Intel 750 and Samsung drives flattened the competition, as would any PCIe SSD card. They aren't the only PCIe players in the game. OCZ, Hyper-X and Mushkin all have PCIe cards/drives. The SATA III interface with its 6Gbps interface has no prayer against a PCIe 3.0 interface. Even at four lanes, a PCIe card has 31Gbps of throughput, well beyond SATA III.

Main takeaways

1. There is no competition to PCI Express. The only time the other drives were remotely competitive was IOPS measured by SiSoft Sandra, but everything else is miles away. Curiously, PCIe drives have a much slower write speed than read, while the SATA drives are much closer in read/write speed.

2. M.2 is only slightly faster in SATA form over the traditional SATA interface. The beauty of M.2 is its tiny size. Notebook makers should standardize on this interface ASAP.

3. SATA III is pretty much maxed out. Look at my 3-year-old Vertex vs. the ARC and Vector drives. All three are pretty much equal with a few exceptions, even though the ARC and Vector are using newer, faster memory chips. Why is the old 25nm NAND in the Vertex competitive with 19nm NAND? Because that 6Gbit SATA interface is the choke point.

4. Benchmarks don't tell you everything. While testing the Intel 750, I had to do a major update to Windows 10. It stalled at 56% for more than three minutes. So even the fastest drive won't necessarily speed up a slow software process.

Conclusions

Benchmarks test throughput, not regular use. If you are a Word/Excel/Outlook/browser user, you will gain nothing from the Intel 750 over the ARC 100. For office workers, a SATA drive is more than sufficient.

That said, it's clear SATA has reached a throughput dead end. In more tests than not, my old drive performed as well as brand new drives despite age and different operating systems. Many technical sites have been saying for a while that the SAT III bus is maxed, and these tests bear it out, as three new SATA drives all had scores relatively close.

In my opinion, M.2 has its future in laptops. The device is tiny, taking up far less room and weight, not to mention not needing to snake power and SATA cables around the inside of the device. The Crucial drive is more than adequate for notebooks and it sells for $182.99 on NewEgg.

However, analysts from IHS and Gartner alike tell me that M.2 uptake is slow because OEMs still want the option of adding a regular SATA drive. Some OEMs are adopting M.2, just not at a rapid pace. So look carefully when you are laptop shopping to see if they offer it. Having just done a hard drive replacement on a Dell laptop, I can tell you that M.2 replacements should be as easy as a memory upgrade.

The future for desktop performance is definitely NVMe drives, even if they can be a pain in the butt to set up. The question is, do you need it? If you are an office worker, then the answer is no. PCIe-based SSDs are for high-performance situations. Unless you are doing disk-intensive work, these drives are overkill, even as they come down in price.

And as I noted earlier, they can't speed everything up. Without a doubt the slowest part of the testing process was updating Windows 10 after the initial install. Every update was different, owing partly to net congestion and also just getting stuck doing the upgrade process. So an SSD won't make everything faster.

SSDs have become incredibly affordable. Three years ago, I paid $640 for my 512GB Vertex drive. Now, faster SATA drives of the same capacity are less than $200 and the Intel 750 is well below $1 per gigabyte. For several years, people would use a SSD as the C: drive and a large, traditional HDD as a D: for storage. With 1TB SSDs now costing less than $300, you won't need to split things across two drives any more, as 1TB should be sufficient in many use cases, especially in a laptop.

And an SSD upgrade can make even a clunky, low-end laptop much more pleasant to use. After the tests were done, I installed the ARC100 in my laptop, which was a few years old and low-end when I bought it. The difference was night and day and my once-sputtering laptop now zips along like a top of the line laptop.

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There is a flood of new drives coming and 1TB is becoming the upper limit. Three years ago, 512GB was the upper limit and they cost more than a 1TB does now. At CES this past January, OCZ showed off a PCIe SSD called RevoDrive 400 that comes mounted on a PCI Express card, or you can use it on a motherboard with a PCIe-based M.2 slot. It boasts read speeds of 2.4GBps and write speeds of 1.6GBps and comes in 128GB, 256GB, 512GB, and 1TB capacity.

And SanDisk has its own high capacity M.2 drives, the X400, which will come in 128GB, 256GB, 512GB, and 1TB capacity as well as a 2.5-inch SATA drive. So M.2 drives are getting larger capacity while retaining their super small form.

So the future is definitely SSD, especially with memory so cheap, and new form factors will increase performance. With SATA drive prices now below $0.50 per gigabyte, there's really no reason to have a spinning hard disk for your C: drive, or for that matter, even your data drive.

Patrizio is a freelance writer. He can be reached at andypatrizio@gmail.com.