|OCZ RevoDrive X2 PCI-Express SSD|
|Reviews - Featured Reviews: Storage|
|Written by Olin Coles|
|Friday, 19 November 2010|
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SandForce PCI-E SSD Anatomy
The SandForce SF-1200 SATA-3GBps controller is a durable component. SandForce features DuraClass technology on their SF-1200 processor, which claims to provide best-in-class endurance, performance, and lower power consumption. DuraWrite technology extends the endurance of MLC-NAND memory by providing at least five year lifecycles measured with 3000-5000 cycle MLC flash. Additionally, SandForce RAISE technology provides RAID-like protection for single SSD computer systems, and data is secured with AES-128 automatic encryption.
It's easy to mistake the OCZ RevoDrive X2 as merely having four SandForce SF-1200 SSDs combined into RAID-0, which oversimplifies things. There are two primary components to the average SandForce-driven SSD: a single storage controller and flash memory. The OCZ RevoDrive X2 is comprised of four primary components: PCI-Express bridge, RAID controller, dual storage controllers, and flash memory. Some might consider these differences minor semantics, but in truth they contrast a simple storage device (SSD) against a more complex RAID system on the PCI-Express platform.
The first evidence that this isn't your average SSD comes when you boot-up the computer and are given the opportunity to enter the Silicon Image RAID Configuration Utility. Since the SiI3124 chip used on RevoDrive series is identical to those used on many desktop motherboards and RAID controllers, users will find it very familiar. The OCZ RevoDrive has two 'drives' permanently attached, so many of the RAID options are available but unusable (RAID-5/10). Users can destroy the RAID set and rebuild it using smaller or larger stripe sizes, although our SandForce SF1200 RAID-0 SSD Performance article has demonstrated that larger stripes are better for SSDs.
Silicon Image SiI3124 RAID Configuration Utility
When the OCZ RevoDrive X2 SSD is installed into a Windows 7 (64-bit) computer system as a secondary drive, the device manager prompts for driver installation which indicates a lack of Plug-n-Play compliance. OCZ includes the necessary SiI3124 drivers with the RevoDrive series SSD kit, as well as their website. As of November 2010 these drivers were identical to the latest package available direct from Silicon Image (si3124r5_15230_x64_Logo).
Windows 7 Device Manager
SandForce-driven SATA SSDs are capable of connecting to various controller hosts, such as those from Marvell or Intel, which retain TRIM garbage collection functionality as well as AHCI mode features. SandForce-driven PCI-Express form factor devices have their own host controller, and lose this functionality as a result. This is why the SandForce PCI-E SSD anatomy becomes important to understand.
The Pericom PI7C9X130 PCIe-to-PCIx reversible bridge chip is straight-forward in purpose and functionality, as it connects the PCI-Express x4 port to one standard 64-bit /133 MHz PCIx port which messages the Sil3124 RAID controller chip. This is where the magic happens, as Silicon Image defines their SiI3124 chip as a PCI-Express to SATA-3GB/s controller capable of driving four ports. The current version of OCZ's RevoDrive X2 SSD incorporates the Sil3124 chip to drive two of the four available channels, using four SandForce SF-1200 controllers combined into a RAID-0 array to produce peak performance before reaching a collection of NAND flash components.
SiI3124 Block Diagram (Courtesy Silicon Image)
The SATA 3Gb/s SandForce SF-1222TA3-SBH processor utilizes a Tensilica Diamond Core DC_570T internal CPU. SandForce-driven SSDs include either a SF-1200 processor for retail consumer products, or the SF-1500 for enterprise storage devices. While all SandForce SSDs offer native TRIM garbage collection (Microsoft Windows 7), Native Command Queuing (NCQ) with 32 command slots, and Self-Monitoring, Analysis, and Reporting Technology (SMART) command set, they cannot be passed-through to the Silicon Image SiI3124 RAID chip with current driver support unlike Intel's ICH10 does with the Rapid Storage Technology software. Regardless, the SF-1200 controller does an excellent job of minimizing re-write delays associated with dirty NAND.
SandForce SF-1222TA3-SBC Processor
A key benefit to SandForce's SF-1200 architecture is that the SSD keeps all information on the NAND grid and removes the need for a separate cache buffer DRAM module by using the SandForce DuraClass technology. This results in a faster transaction, albeit at the expense of total storage capacity. SandForce SSDs also utilize over-provisioning technology, which allocates a portion of NAND for data storage and the remainder reserved for transaction and cache buffer space.
The SF-1200 SSD processor provides ECC data protection and includes SandForce's unique RAISE (Redundant Array of Independent Silicon Elements) technology. RAISE provides the protection and reliability of RAID on a single SSD drive, thanks to flash architecture, without the significant write overhead of parity. The SandForce DuraClass technology automatically stores data in AES-128 encrypted format, preventing data extraction directly from the physical flash memory modules.
Intel 29F64G08CAMDB NAND Flash IC
Several multi-layer cell (MLC) Intel 29F64G08CAMDB NAND flash modules are joined to the SandForce SF-1200 controllers. On the 240GB RevoDrive X2 SSD model these NAND modules combine for 256GB of physical storage space, yet only 240GB of this capacity is designated for data. Consumer-level SandForce SSDs receive 7% over-provisioning which is why 128GB devices will yield 120GB of usable storage space.