OCZ Announces First SATA Host Managed SSD: Saber 1000 HMS

Today OCZ is introducing the first SATA drive featuring a technology that may be the next big thing for enterprise SSDs. Referred to by OCZ as “Host Managed SSD” technology (HMS) and known elsewhere in the industry by the buzzword “Storage Intelligence”, the general idea is to let the host computer know more about what’s going on inside the SSD and to have more influence over how the SSD controller goes about its business.

Standardization efforts have been underway for more than a year in the committees for SAS, SATA, and NVMe, but OCZ’s implementation is a pre-standard design that may not be compatible with what is eventually ratified. To provide some degree of forwards compatibility, OCZ is releasing an open-source abstraction library to provide what they hope will be a hardware-agnostic interface that can be used with future HMS devices.

OCZ’s HMS implementation provides a vendor-specific extension of the ATA command set. A mode switch is required to access HMS features; when HMS mode is off the drive behaves like a normal non-HMS SATA drive and all background processing like garbage collection are managed autonomously by the SSD. When the HMS features are enabled, the host computer can request that the drive override normal operating procedure and disable all background processes, or to perform them as a high-priority task. If background processing is left disabled for too long, the drive will re-enable the background processing when needed and suffer the immediate performance penalty of the emergency garbage collection.

The intention is to allow better aggregate performance from an array of drives. An example OCZ gives is of an array divided into three pools of drives. At any given time, two pools are actively receiving writes, while the drives in the third pool are focusing solely on the “background” housekeeping operations. The two pools that are in active use defer all the background processing and operate with peak performance and consistency. By cycling the drive pools through the two modes, the intention is that none of the active drives will ever reach the steady-state of having constant background processing to free up space for the incoming writes. This provides a big improvement to performance consistency, and can also provide a minor improvement to overall throughput of the array.

Obviously, the load balancing and coordination required by such a scheme is not part of any traditional RAID setup. OCZ expects early adopters of HMS technology to make use of it from application layer code. HMS does not require any new operating system drivers, and OCZ will be providing tools and reference code to facilitate using HMS. They plan to eventually expand this to a comprehensive SDK, but for now everybody is in the position of having to explore how to best make use of HMS for their specific use case. For some customers, that may mean load balancing several pools of SSDs attached to a single server, while others may find it easier to temporarily offline an entire server for housekeeping.

OCZ has also envisioned that future HMS products may expand the controls from managing background processing to also changing overprovisioning or power limits on the fly, but they have no specific timeline for those features.

The drive OCZ is introducing with HMS technology is a variant of their existing Saber 1000 enterprise SATA SSD. The Saber 1000 HMS differs only in the SSD controller firmware; otherwise it is still a low-cost drive using the Barefoot 3 controller and is intended primarily for read-oriented workloads. Pricing is the same with or without HMS capability, though the Saber 1000 HMS is only offered in the 480GB and 960GB capacities. The warranty in either case is limited to 5 years, but because the HMS controls can affect write amplification, the Saber HMS write endurance rating is based on the actual Program/Erase cycle count of the drive rather than the total amount of data written to the drive.

As a read-oriented drive with relatively little overprovisioning, the Saber 1000 has a lot to gain from HMS in terms of write performance and consistency, and it may allow the Saber 1000 HMS to compete in areas the Saber 1000 isn’t fast enough for.

In addition to control over the garbage collection process, the Saber 1000 HMS provides a similar set of controls for managing when the controller saves metadata from its RAM to the flash. This is the information the controller uses to keep track of where each piece of data is physically stored and which blocks are free to accept new writes. Every write to the disk adds to the metadata log, so the changes need to be periodically evicted from RAM to flash. This is one of the key data structures that the drive’s power loss protection needs to preserve, so the size of the in-RAM metadata log may also be limited by the drive’s capacitor budget.

To enable software to make effective use of these controls, the Saber 1000 HMS provides an unprecedented view in to the inner workings of the drive. Software can query the drive for the NAND page size, erase block size, number of blocks per bank and number of banks in the drive. The total program and erase counts are reported separately, and information about free blocks is reported as the total across the drive as well as the average, maximum, and minimum per bank. The drive also provides a status summary of whether garbage collection or metadata log dumping are active, and whether they are needed. OCZ’s reference guide provides recommendations for interpreting all of these indicators.

The Saber 1000 HMS will be available in early November for bulk purchases. The technical documentation and reference code should be available online today.

The Plextor M6V (256GB) SSD Review

Plextor’s M6V SSD was originally planned to be their first drive using TLC NAND, but that has now been put off to next year’s M7V. Instead, Plextor is taking advantage of a surprise hit in the SSD controller market, Silicon Motion’s SM2246EN controller, to produce a budget SSD using Toshiba’s 15nm MLC NAND.

Micron acquires SSD Controller Designer Tidal Systems, Inc.

A year ago, several veterans of SSD controller design firms SandForce and Link_A_Media Devices formed a new startup called Tidal Systems, Inc. to focus on developing NVMe SSD controllers. Tidal has spent the past year operating in stealth mode, and their website has almost no information about the company’s work.

Over this past week, during a financial call to investors, it was announced that Tidal has now been acquired by Micron. There are no details available regarding the acquisition and Micron reported their quarterly results just before the acquisition so we won’t get any more information soon. On the technical side, Micron plans to fold Tidal into their Advanced Controller Group and use Tidal controllers in client PCIe SSDs.

While the news that the acquisition has been floating around for a few days, we wanted more and so contacted Micron’s PR to get further information about the acquisition. Ultimately we were told very little as the details are being kept under wraps for the time being. We were told that the acquisition includes Tidal’s “inventory, equipment and intellectual property rights”; not mentioned in our discussions with Micron were the key people involved in developing Tidal’s technology. Some amount of staff turnover during an acquisition is normal, and we’ll have to wait and see who stays with Micron or gets put up the chain. Neither company has given an indication of how close to market Tidal’s controller/controllers (we don’t even know how many are involved here) may be, so it is difficult to gauge how much of an impact, both in terms of technology and personnel, this acquisition will have.

This acquisition is motivated by Micron’s desire to develop high-end client SSDs without being dependent on third-party controllers from Marvell or others. This would give Micron more opportunity for product differentiation and keep more of the design in-house. This is becoming important as consolidation takes place – vertical integration of the SSD business has been working out very well for Samsung and Intel, and the industry has seen a lot of the consolidation ethos in recent years. Micron’s acquisition leaves SanDisk as the only NAND manufacturer that doesn’t do in-house controller design for the client SSD market, so it’s likely that they’re is sizing up the remaining independent SSD controller vendors.