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Intel's 320 Series solid-state drive


Back to the next generation
— 10:00 AM on March 28, 2011

In the world of solid-state drives, Intel reminds me a little of Jon Jones. Yes, I'm going there. From very early on, it was clear that the UFC's new light-heavyweight champion had the combination of genetics and talent to become something special in the sport of mixed martial arts. With a tall frame and long limbs, Jones had the reach to strike opponents from well outside their range. Freakish athleticism and exceptional wrestling allowed him to keep the fight standing or to ragdoll victims to the ground. The pieces were there, and he put them together pretty quickly.

The pieces that make Intel a perfect fit for SSDs aren't quite as flashy, but they're no less tailored for this burgeoning market. Intel is renowned for its ability to produce high-performance semiconductors using increasingly advanced fabrication techniques, making it an ideal provider of the NAND flash memory chips provide a drive's capacity. Over years of CPU and chipset development, Intel has also earned a reputation for building wicked-fast memory and storage controllers—expertise that no doubt applies nicely to the firmware and controller logic that links banks of NAND dies to a Serial ATA port.

Intel's SSD career started back in September 2008 with the original X25-M, which used the combination of a custom 10-channel storage controller and 50-nano flash to dominate the solid-state alternatives available at the time. In July of 2009, Intel returned to the ring with a second-generation X25-M featuring a tweaked controller design and more advanced memory built with 34-nm fabrication technology. Like its predecessor, the gen-two drive offered better overall performance than its contemporary rivals, cementing Intel's status as a legitimate favorite in the world of solid-state storage.

Earlier this month, the chip giant detoured from the X25-M's evolution to release the Intel 510 Series. Rather than keeping everything in the family, this new high-end model spreads a layer of Intel's own firmware atop the same 6Gbps Marvell controller found inside SSDs from competing manufacturers. Now, just a few weeks after the 510 Series' release, the X25-M is back in a third generation dubbed the Intel 320 Series.


Yep, the Intel 320 Series even looks like an X25-M

Like the X25-M models that have come before it, the Intel 320 Series packs MLC flash memory based on the latest process node in chip fabrication technology. This 25-nm NAND is paired with Intel's existing controller silicon, which has been augmented by firmware tweaks and new capabilities designed with data integrity in mind.

As the 320 model number suggests, the third-generation X25-M is meant to slot in below the high-end 510 Series. Don't get your hopes up for a new standard in storage performance. Intel appears to have focused most of its efforts on improving this drive's reliability and lowering costs. Those strike me as sensible points of focus for a mid-range SSD making the transition to 25-nano flash. As Intel astutely points out, the performance delta between decent SSDs and mechanical hard drives is huge next to the comparatively minor differences in performance between various SSD models. The Intel 320 isn't meant to challenge for the SSD performance crown. Instead, it's looking to lure more folks into the SSD fold.

When briefing the press last week, Intel spent much more time talking about reliability than it did discussing performance. We haven't heard much from SSD makers on this front, but Intel revealed some interesting figures about the X25-M, which has been deployed internally throughout the company. Among the 50,000 drives pressed into service by Intel's IT department, the annual failure rate is claimed to be 0.61%. Intel also quotes a 0.26% failure rate for the over 100,000 X25-Ms in use by ZT Systems, an enterprise customer running the drives in a datacenter environment. For the over 800,000 SSDs that Intel has shipped into the distribution channel, the failure rate is said to be only 0.4%. Since these figures come from Intel, we'll need to add salt—but perhaps only a sprinkle. Earlier this year, a French retailer released reliability stats on hard drive failures. Intel SSDs had a failure rate of 0.59%, while the solid-state competition from Corsair, Crucial, Kingston, and OCZ ranged from 2.17-2.93%.


25-nano flash in all its next-generation glory

Even lower failure rates are expected from the Intel 320 Series, which is at a bit of a challenge given its use of 25-nano NAND. Moving to a smaller fabrication process allows Intel to squeeze more flash dies onto a single wafer, so it's a necessary step toward lowering SSD prices. However, the smaller memory chips are more prone to errors and have less endurance than their 34-nano predecessors, putting Intel's latest at a disadvantage right out of the gate.

Intel has worked closely with Micron on 25-nano flash development, but the processor giant says its testing procedures are completely separate from those of its partner. As it does with CPUs, Intel sorts through all the chips it produces in a process called binning. Flash dies are tested for performance and endurance, and only the best make the cut for inclusion in Intel SSDs. Although you may find Intel-branded flash chips on solid-state drives from other manufacturers, those chips haven't necessarily undergone the same level of testing as the flash set aside for Intel's own drives.

According to OCZ, the 25-nm Micron flash chips in its latest Vertex 3 SSD are good for 3,000 write-erase cycles. Intel declined to divulge the write-erase endurance of the 320 Series' flash chips, but it does offer endurance information for the drive as a whole. The Intel 320 Series is guaranteed to write 20GB of data per day for five years in a consumer environment. With enterprise workloads, the drive is rated for 60TB worth of writes. Those estimates look to be a little conservative given the fact that Micron's own RealSSD C400, otherwise known as the Crucial m4, has 25-nano flash and is said to be capable of writing 72TB of data over its lifetime.


Six less-than-super capacitors flank a DRAM cache

Regardless of how long individual flash cells are supposed to survive, failures are inevitable. The Intel 320 Series protects against any data loss that might occur in this situation by employing "surplus data arrays." Also referred to as XOR—the logical operation often used to calculate parity bits for RAID arrays—this redundancy scheme is capable of recovering data from a failed bit, block, or even an entire failed die. Intel describes XOR as a NAND-level RAID 4, making it sound rather similar to the RAISE technology employed by SandForce controllers.

RAISE is described as more of a RAID 5 than a RAID 4, though. SandForce says RAISE spreads redundancy data across the entire drive, and that the storage capacity lost amounts to the capacity of one flash die. Intel isn't specific about the amount of storage consumed by XOR, but it does say the redundancy data is rolled into the 7% of total flash capacity reserved for use by the controller. According to Intel, XOR is governed by a mix of hardware and firmware that doesn't introduce any performance-sapping overhead. The only time it'll slow the drive down is when data is being recovered in the event of a flash failure.

How often might such a failure occur? Intel says it ran nearly 1,400 drives through a simulated five-year workload. Across all of them, XOR stepped in to recover data a total of 14 times. Thanks to its assistance, only a couple of the Intel 320 Series drives suffered irrecoverable failures. Intel ran the old X25-M through a similar test and had five drives fail, suggesting that the new model should be more reliable than the old one—thanks to XOR. Without the redundancy scheme, those 14 XOR recoveries would have pushed the number of Intel 320 Series failures to 16. Intel does point out that its 320 Series is brand new, while the X25-M is a mature product whose flash has been in production for quite some time now. I'd expect error rates in Intel's 25-nano flash to decrease over the life of the product. In the interim, XOR should provide some peace of mind.

Speaking of peace of mind, the Intel 320 series includes a measure of power-loss protection via a series of small capacitors visible in the picture above. When the drive detects imminent power loss, it disconnects power from the host and transfers data out of its buffers and into the NAND. All other activities are de-prioritized during this time, ensuring that the drive doesn't lose any data when the power cuts out. This particular feature should appeal to the enterprise customers who have apparently become quite fond of the X25-M. Intel says its consumer-grade SSDs have become more popular among enterprise clients than the X25-E it designed specifically for the market.

Another Intel 320 Series feature that's sure to please corporate types is the inclusion of 128-bit AES encryption. This hardware-based encryption scheme can be invoked by setting an ATA user password, and there's supposed to be no performance impact.