Introducing the Intel X25 (Gen3) Controller
Introducing the Intel X25 (Gen3) Controller
Even though it has been five years since their last in-house controller was released, Intel has been hard at work improving upon previous designs. The end result is the all new X25 which is used inside the DC S3700 line of solid state drives.
Very little is actually known about the physical layout and design of the controller itself. All Intel is willing to share about the architecture is that it is a 100% in-house proprietary design, using custom in-house firmware. However, Intel may not be willing to give specifics on the core’s primary components they were more than willing to share feature-specific details.
The most obvious departure from previous designs is the new X25’s use of 8 channels rather than the previous generation’s 10-channel layout. 8 channel designs have become the de-facto standard for the industry and in all likelihood Intel went with slightly less pathways to help reduce latency. Much like OCZ’s Barefoot 3 controller, latency, long term sustained performance and durability are the three central domains which Intel wanted to improve upon.
On the latency front, Intel states that 99.9% of the time average latency will be less than .500ms. This is a 50% reduction in read latency compared to the 710’s specification of .75ms. When compared against the impressive 910 PCI-E SSD’s specification of .65ms it still is 23% faster.
The IOPS performance of this controller also has been greatly increased as well. The Intel 910 800GB requires a quartet of controllers to hit its peak 180K read / 75K writes IOPS specification, whereas a single DC S3700 800GB has 75K read / 35K writes IOPS. Just as importantly this maximum 75,000 / 35, 000 IOPS rating is much closer to the DC S3700’s sustained real world performance than any other device available. In fact, while most other enterprise-class drives claim potential IOPS performance variation of 20% from one drive to the next, Intel has reduced that number to a mere 15% or less. This allows server and storage administrators to more accurately judge how many devices they will require to meet expected demand.
Increased performance with decreased latency is all well and fine but what really makes the DC-S3700 distinctive is the fail safes it has in place to ensure data safety. All controllers implement certain a level of checks and balances to ensure data integrity but the new Intel X25 and the DC S3700 takes this approach to entirely new levels. The Uncorrectable Bit Error Rate (UEBR) is actually an unheard of 1 bit in 10 to the 17th power, which is 10 times greater than the previous generation 710 or even the Intel 910’s 1 in 10 to the 16th UEBR. To put this into understandable terminology, Intel expects there to be a single unrecoverable bit error in every 12.5 Petabytes of data read.
The X25 is able to offer such high levels of dependability due to the comprehensive data protection routines it uses under the auspices of Intel’s Stress Free Protection. At its most basic, this philosophy of end to end protection starts with over provisioning. Much like the original SandForce series, Intel has chosen ~20% of over-provisioning for their new controller. In the 200GB model this is 40GB while the 800GB model uses a whopping 160GB to ensure a failsafe partition is maintained.
This spare area can be used for everything from bad block replacement to garbage collection. It also allows for more consistent long term performance as the controller will always have access to free blocks to use for wear leveling even when the drive is nearing full capacity.
Like the previous generation X25 controller, this new iteration makes use of auto-encryption with AES routines which have now been upgraded from 128-bit to 256-bit. By default, Intel has disabled AES encryption but it can be initiated via software on a case by case basis. This added flexibility allows the controller to be more adaptable to the needs of individual clients. Using the built in AES encryption routines will impart a certain amount of performance loss due to increased overhead, but there are scenarios where this is a trade-off well worth making.
The X25 G3 also uses BCH error correction algorithms. However, unlike any other controller, the X25 G3 writes parity data to the NAND and does ECC on the memory rather than solely focusing upon the primary storage environment.
All these features are fairly typical for modern controllers, albeit at the higher end of the scale. However, Intel has not stopped at basic levels to ensure data safety. They’ve stepped up the game by double and triple checking nearly every segment of data. So much so that a ‘simple’ write request to the NAND looks like this: a CRC is created along with the DATA, the DATA + CRC is then written to the NAND, an LBA tag is then created, then a parity bit is also written and checked. Finally, during read IO requests the additional data protections are all read – including ECC on the memory - to ensure the data is safe and reliable.
If at any time a check fails, the controller will notify the system host controller to recover the data via its own ECC. Should this happen, the administrator is instructed to removed the drive from the RAID array, replace it with a new one and RMA the failing drive. Meanwhile, all of the data would be saved on other segments of the array.
On top of all this, at standard intervals –during low IO periods, boot up, etc - the controller will also routinely check the status of all onboard capacitors. If they fail the self test, the controller will automatically disable the write buffer and notify the system’s host controller of the issue.
It is worth noting that the controller does not treat its internal NAND as an array. Rather, it treats the ICs as “one” logical unit so there is no equivalent of LSI SF2281’s RAISE (Redundant Array of Independent Silicon Elements) being implemented meriting such extreme error recovery procedures.
Taken as a whole, this high performance controller is highly adaptable and much more capable than either any of its predecessors or any other controller on the market today. It certainly should make a great addition to Intel’s current stable of high performance RAID-oriented drives.
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