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Intel's 750 Series solid-state drive reviewed

PCIe storage pillaged from the datacenter

PC enthusiasts have a proud tradition of appropriating enterprise-class hardware for personal systems. Stuffing server-grade gear into a desktop can improve performance dramatically in some cases. It also unlocks immediate bragging rights over systems equipped with more pedestrian hardware.

Although hardware makers tend to frown at this practice, some have adopted it as their own. Intel, for example, has long fueled its high-end desktop platform with parts pulled from the server and workstation world. Haswell-E and its predecessors are really just Xeon CPUs repurposed for desktop use—and packaged specifically with enthusiasts in mind. The company's storage division has been getting in on the action, too. Last year, it introduced a 730 Series SSD that's basically a rebadged datacenter drive with a few tweaks under the hood.

The 730 Series is pretty sweet, but it's tied to a Serial ATA interface and AHCI protocol that can't keep up with modern flash memory. That's why Intel's latest datacenter drives use a faster PCI Express interface backed by an SSD-specific NVM Express protocol. This new family hit servers last summer, and today, it migrates to the desktop as the 750 Series.

Under the hood, the 750 Series features the same controller as its datacenter counterparts. This proprietary Intel chip has an eight-channel NAND interface at one end and four lanes of PCIe Gen3 goodness at the other. It's meant to connect directly to PCIe lanes in the CPU rather than through an intermediary chipset on the motherboard. (Intel's 9-series chipsets are limited to Gen2 speeds, so they're not fast enough to keep up.)

Four lanes of PCIe Gen3 connectivity offer up to 4GB/s of theoretical bandwidth, which is well above SATA's top speed—and comfortably beyond the bandwidth of the dual-Gen2 M.2 slots on most motherboards. A wider pipe is only one piece of the puzzle, though. The controller is also based on the NVM Express protocol designed to replace SATA's ancient AHCI spec.

Watch our discussion of the Intel 750 Series and other PCIe SSDs on the TR Podcast

AHCI was architected for hard drives based on mechanical platters. Those drives are a low-speed, high-latency proposition compared to the massively parallel NAND arrays behind modern SSDs. NVMe was designed from the ground up for solid-state storage, so it lacks legacy baggage from the mechanical era. It promises better performance through lower overhead and greater scalability. Where AHCI is limited to a single command queue 32 entries deep, NVMe supports up to 64k queues with 64k entries each.

Intel says the 750 Series achieves peak performance at a queue depth of 128, which is much more than AHCI can muster yet well short of NVMe's maximum capacity. That's probably a good place to be at such an early stage in the protocol's life.

Capacity Die config Max sequential (MB/s) Max Random (IOps) Price $/GB
Read Write Read Write
400GB 28 x 16GB 2200 900 430k 230k $389 $0.97
1.2TB 86 x 16GB 2400 1200 440k 290k $1029 $0.84

PCIe and NVMe combine to give the 750 Series crushing performance stats for both sequential and random I/O. The flagship 1.2TB config hits 2400MB/s, according to the spec sheet, quadrupling the maximum speed of Serial ATA. Versus last year's 730 Series, the new hotness is specced for severalfold performance gains on all fronts. You don't lose too much dropping to the base 400GB model, either.

Although the 750 Series doesn't match the 2800MB/s sequential peak of Intel's top datacenter SSD, the DC P3700, it does beat that drive's random write rating. Credit the firmware, which contains "radical" changes focused on improving random I/O performance. The firmware is also configured to allocate 8-9% of the drive's total flash capacity to overprovisioned area. That's similar to the overprovisioning in typical consumer drives but less than the ~25% set aside by the P3700.

Like its enterprise forebear, the 750 Series uses 20-nm NAND fabbed by Intel's joint flash venture with Micron. The chips weigh in at 16GB apiece, and they're a lower grade than the top-shelf bin reserved for the P3700. The drive's endurance rating is much lower as a result, but it's still more than sufficient for typical consumer usage patterns. The 750 Series is rated to absorb up to 70GB of writes per day over the length of its five-year warranty.

There are no guarantees after the drive's endurance spec is exceeded, but the 750 Series should be able to write a lot more data before reaching the raw cycling limit of its NAND. (The Intel 335 Series in our SSD Endurance Experiment wrote over 700TB before hitting that media wear threshold.) When the NAND's limits are reached, the 750 Series is designed to slip into a "logical disable" mode that throttles write speeds severely enough to produce an effective read-only state. Intel's other consumer SSDs are programmed to brick themselves at the next reboot, preventing users from accessing their data. The 750 Series instead emulates its enterprise counterparts, which remain in read-only mode through subsequent reboots.

Like its server-oriented siblings, the 750 Series comes in two form factors. The half-height, half-length add-in card pictured on the left slots into standard PCIe slots, and Intel throws in a full-height backplate for typical desktop enclosures. The 2.5" version on the right is meant for traditional drive bays, though its 15-mm thickness requires more headroom than most SSDs.

Both variants use prominent heatsinks to cool the controller and NAND. The 750 Series is rated for peak power draw of 25W, so there's a lot of heat to dissipate. Thanks to these hunks of finned metal, the drive is rated to withstand ambient temperatures up to 70°C, an important consideration for systems crowded with multiple graphics cards and other high-end components.

Instead of connecting via PCIe slot, the 2.5" unit has an SFF-8639 jack and associated cabling. Intel ships the drive with an 18" shielded cable from a company called Amphenol. This cable pipes signaling and clock data for the quad PCIe lanes to a smaller, square-shaped SFF-8643 connector that plugs into the host system. Instead of drawing power from that connection, the cable pulls juice from a standard PSU SATA connector.

The cabled solution purportedly delivers identical performance to the add-in card. It also leaves PCIe slots open for multiple graphics cards, which is why Intel believes the cabled version will end up being more popular than the card.

Intel says the SFF-8643 host connector can be mounted on motherboards in numerous orientations, including an edge-facing config to facilitate clean cable routing. We haven't seen any motherboards with the requisite SFF jack onboard, though. Asus' new Sabertooth X99 does come with a compatible connector, but the port lives on a bundled adapter card rather than on the motherboard itself. It may take some time before truly native implementations arrive.

Even with the add-in card, motherboard firmware still needs the right hooks to boot from the 750 Series and other NVMe SSDs. Intel has been working with the major firmware vendors to integrate support for NVMe drives, and UEFI version 2.3.1 has everything that's required. Motherboard makers have to roll that revision into the firmware for their individual products, of course, but Intel tells us all Z97 and X99 boards should have access to the necessary update. Depending on the firmware, older UEFI-based boards may also work with the 750 Series.

Once you have a compatible motherboard, the next requirement is an operating system with NVMe support. Windows 8.1 has native drivers built in, and Win7 adds them via hotfix. Intel offers its own NVMe drivers, as well, and it claims they're faster than the ones Microsoft supplies. We used the Intel drivers for all our testing. Speaking of which, let's dig into the performance analysis on the next page.