Anandtech has just posted a meaty article about SandForce SSD controllers as used in SSDs from OCZ and Corsair. (Understanding SandForce's SF-1200 & SF-1500, Not All Drives are Equal) It’s worth a read from at least two perspectives. First, it gives you some pretty deep insight into the real importance and value of the firmware running on these SSD controllers. As the Anandtech article discusses, controller firmware can make a substantial performance difference using the same hardware. In the case of the SandForce SF-1500 enterprise SSD controller and the company’s SF-1200 “client” SSD controller chips, firmware makes all the difference in performance because the two devices are electrically the same IC. Both chips running their associated firmware are rated at 30K random-read IOPS (I/O operations per second for 4-Kbyte reads) but the SF1500 is rated at 30K random-write IOPS (4-Kbyte writes) while the SF-1200 is rated at 10K random-write IOPS, which is a whopping two-thirds less performance than delivered by the electrically identical SF-1500 controller chip. There’s also an order-of-magnitude difference in rated data reliability between the two controllers, which you’d expect customers to want for enterprise-class SSDs. From the perspective of product positioning, this performance spread makes tremendous sense because the enterprise-class SF-1500 is reported to be substantially more expensive than the SF-1200 and the price premium is largely attributable to the differential speed and data-reliability performance delivered by the controller firmware (along with some extra reliability testing for the SF-1500 chip).

As Anandtech reports, because of a special relationship with SandForce, OCZ apparently got a special “fast” version of the control firmware for the SF-1200 controller that delivers the faster random-write IOPS performance of the SF-1500 and OCZ will reportedly be using that controller-chip/firmware combo in an upcoming Vertex 2 SSD. Anandtech further reports that this “fast” SF-1200 firmware reached at least one other SSD vendor, Corsair, through an early firmware release. Anandtech has tested an early review version of this drive and it delivers the higher performance. A later production version of this controller firmware apparently does throttle the SF-1200’s write IOPS performance to the rated “client”
SSD levels.

Despite Anandtech’s stated concerns, all this versioning and throttling isn’t anything particularly new or insidious in the electronics industry. The end customer pays for performance, which is both a real and perceived value, whether or not the performance is due to hardware or firmware differences. From an SSD customer’s perspective, it’s the drive delivering this performance and most customers will not care or even understand the fine distinction between hardware-delivered and firmware-delivered performance. In fact the Anandtech article notes that Intel does a similar thing by enabling or disabling Hyperthreading on two differently priced Core i5 and Core i7 processors. Same die, different performance. I know of a case all the way back in the 1970s where changing one bit in a product’s firmware image doubled the amount of RAM available to the user. Changing that bit cost the customer a few thousand dollars. So the practice isn’t new. But SSD vendors do need to know the difference. They need to understand the cost/performance tradeoffs they are making, because their products’ performance will reflect the consequences of these choices.

Thus the point of this blog entry is to point out, perhaps even to underscore, that firmware is a big differentiator in SSD performance, just as it is in just about any product category. SSD vendors need to understand this. Companies developing SSD controller chips should be aware that excellent controller firmware can substantially differentiate products, just as it has for SandForce’s SF-1500 and SF-1200 controllers. SSD manufacturers should be ready to grill their controller vendors about the supplied firmware. Is it as good as it can be? Could it be faster? Very good questions to ask as the SSD competitive landscape continues to heat up. SSD controller-chip vendors: be prepared.

Geoff Gasior at The Tech Report has just published a long and very comprehensive side-by-side comparison of four SSDs from Corsair, Kingston, Plextor, and Western Digital. He’s pulled the covers off the drives to look at the guts (and he names names of the on-board controller chips in the process) and Gasior then tests each drive in turn to come up with some really interesting comparisons. If you’re interested in how SSDs are being and will be tested and want to see some surprises in the differentiated results, be sure to read through the entire 10-page article. For the more impatient, here are some key points made in the review:

Controller chips

One of the really interesting elements of the review is a description of each design’s architecture including the controller chip used. Here’s a summary:

Corsair Nova V128 (128 Gbytes)
Controller chip: Indilinx Barefoot ECO
NAND Flash: 16 MLC chips from IM Flash

Kingston SSDNow V+ (128 Gbytes)
Controller Chip: Toshiba T6UG1XBG
NAND Flash: 8 MLC chips from Toshiba

Plextor PX-128M1S (128 Gbytes)
Controller chip: Marvell "Da Vinci" 88SS8014
NAND Flash: 16 MLC chips from Samsung

Western Digital SiliconEdge Blue (256 Gbytes)
Controller chip: JMicron JMF612
NAND Flash: 32 MLC chips from Samsung (double stacked)

The diversity of the controllers and the differing quantities of on-board NAND Flash chips results in a diverse set of I/O performance specs for the drives:

Corsair Nova V128
Rated read speed: 270 Mbytes/sec
Rated write speed: 195 Mbytes/sec

Kingston SSDNow V+
Rated read speed: 230 Mbytes/sec
Rated write speed: 180 Mbytes/sec

Plextor PX-128M1S
Rated read speed: 130 Mbytes/sec
Rated write speed: 70 Mbytes/sec

Western Digital Silicon Edge Blue
Rated read speed: 250 Mbytes/sec
Rated write speed: 170 Mbytes/sec

Take some time to read through the article. Pay particular attention to the well-written discussion of the TRIM command, which is implemented on all of the above drives except for the Plextor drive.

This article is a good example of how people will be evaluating SSDs in the future. Unlike mechanical HDDs, where the read/write performance is largely set by the rotational speed of the spinning platters regardless of the drive vendor or the built-in controller chip manufacturer, SSD performance is very much a function of the NAND Flash parallelism in the drive’s architectural design, the SSD’s controller chip’s design, and the effectiveness of the firmware running on that controller chip. Based on the article’s results, you can see that there’s quite a bit of flexibility in play with respect to SSD performance and that the innovations put into the drive will be sussed out by advanced customers.

PCWorld reports that Micron will soon be rolling out Enterprise-class SSDs based on 34nm, ONFI 2.1, SLC (single-level cell) NAND Flash devices. These drives will employ the 6-Gbit/sec SATA 3.0 interface specification to create an I/O channel with enough bandwidth to support the faster Flash. Doing so makes the soon-to-be-introduced RealSSD P300 SSDs more than competitive with 10,000- and 15,000-rpm Enterprise-class HDDs, which may employ 6-Gbit/sec SATA 3.0 interfaces but cannot fully utilize the improved bandwidth because they simply cannot get the data off the read/write heads fast enough. The inherent scalable parallelism of SSD architectures makes it far easier for SSD designers to bump data bandwidth at will.

Micron will reportedly sell the P300 drives in capacities of 50, 100, and 200 Gbytes. These drives will replace the company’s current RealSSD P200 drives, which deliver sequential read speeds of up to 180 Mbytes/sec and write speeds of up to 115 Mbytes/sec while a fully saturated SATA 3.0 interface theoretically delivers a maximum bandwidth of 750 Mbytes/sec. Practical overhead issues will reduce the maximum effective bandwidth somewhat, but SATA 3.0 can clearly deliver far more throughput than currently achieved by Micron's P200 SSDs. One key to this boost is the faster ONFI 2.1 NAND Flash interface.

In contrast to short-stroked, high-rpm HDDs that require a lot of power and consequently require a lot of cooling, Enterprise-class SSDs draw far less power and require almost no cooling compared to high-rpm HDDs, so there are considerable cost considerations beyond hopelessly simplistic cost/Gbyte metrics when considering SSDs for enterprise-class storage. In addition, SSDs have predictable reliability characteristics that can help data centers avoid catastrophic storage failures in mission-critical applications such as finance and online commerce.

Guest Blogger: Marc Greenberg, Technical Marketing Director

By now it seems that anyone with an engineering degree has probably read 2 or 3 teardown reports on Apple’s iPad. Few that I have seen so far talk about the DRAM memory subsystem – and that could be because the DRAM was hidden on top of Apple’s A4 processor.

Chipworks.com has torn down Apple’s A4 processor package and reports that the DRAM subsystem consists of two Samsung LPDDR1 1Gbit memories in package-on-package (PoP) configuration. The PoP allows for the DRAM to sit on top of the application processor and the whole thing has been marked on top with Apple’s A4 logo. There’s a great cross-sectional photo of the PoP system showing the A4 processor underneath and the two DRAM dice on top.

It’s no secret that the iPad has a substantial amount of MLC NAND flash, but the interesting thing for me was Apple’s continued reliance on first generation Low-Power DDR1 (LPDDR1) technology instead of latest-generation LPDDR2. LPDDR1 technology was introduced in 2003 making this one of the oldest technology standards in use in the iPad.

Several applications processors already support LPDDR2:
- ST-Ericsson U8500
- Freescale i.MX508
- TI OMAP4
- Broadcom BCM2763
- Samsung S5PC100

Plus a bunch of others that we at Denali know about but which are not public yet.

The specific DRAM in use in the iPad appears to be a Samsung K4X1G323PE according to this die photo. According to the part decoder, we can see this is a 1Gbit X32 4 bank LPDDR1 device with 1.8v IOs. Samsung’s Mobile DDR (LPDDR1) product list indicates that the maximum speed of operation of this die is 200MHz (DDR400).

Even though LPDDR1 was introduced in 2003, the 1Gbit LPDDR1 parts are a relatively recent introduction, and the mask date code on the die photo is September 2008. Relying on 1.8V signaling, LPDDR1 has higher operating voltage than DDR3 (1.5v), DDR2L (1.5V), DDR3U (1.2xV) and LPDDR2 (1.2v). LPDDR1 also has the lowest maximum operating frequency of any of the DDR DRAM technologies commonly in use today (DDR2, DDR3, and LPDDR2). LPDDR1 does have lower standby power than any of the DDRx technologies however, surpassed only by LPDDR2.

LPDDR1 definitely has its place in applications that don’t need all the LPDDR2 bandwidth and which also need less memory capacity and low standby power. But for a mobile computing-intensive device like the iPad, LPDDR2 would have been an obvious choice. Among the benefits of LPDDR2 are that LPDDR2 offers lower voltage operation (and thus less power), more flexible power management modes, fewer package pins (less costly packages), and higher frequency of operation (more bandwidth) in comparison to LPDDR1. LPDDR2 is specified for up to 533MHz/DDR1066 operation and new designs are commonly specifying up to double the LPDDR1 frequency.

LPDDR2 also has the unique property of supporting Non-Volatile Memory (NVM) such as Phase-Change Memory (PCM) on the same bus as LPDDR2 DRAM. This LPDDR2-NVM offers similar performance to DRAM but with less operating power and near-zero standby power and also offers faster system boot and resume from suspend times.

The question is, why did Apple not choose the latest generation LPDDR2 parts for the iPad? It could be a couple of reasons. They may not have been able to source 600,000 LPDDR2 dice in time for the launch. The LPDDR2 parts may be at too much of a cost premium. It could have been a hang-over from the iPhone. Or there could be a marketing answer: Apple may have designed the A4 to work with LPDDR1 or LPDDR2 technology. That would allow a later version of the iPad to use LPDDR2 to provide longer battery life and more performance – enough for multitasking, perhaps?

Whatever the case may be, LPDDR2 is an available option on high-end application processors and is ready for all kinds of new designs. Denali has offered LPDDR2 memory models since the early part of 2008 and was making customer deliveries of Denali’s Databahn LPDDR2 memory controllers at the end of 2008. Today, Denali offers high-performance and low-power memory controllers and PHYs for any combination of DDR1, DDR2, DDR2L, DDR3, DDR3L, DDR3U, LPDDR1, LPDDR2-DRAM or LPDDR2-NVM.

Find out all the latest information on DRAM technology at Memcon, July 28th in Silicon Valley: www.memcon.com

Thanks,

Yesterday, high-performance PC component developer and vendor OCZ Technology rolled out its 4th generation of PCIe-based SSD drives called the Z-drive R2 SSD. The new drives employ NAND Flash memory DIMMS arrayed on a standard PCIe-format add-in card. The cards employ x8 (8-lane) PCIe interfaces to achieve a rated read speed of as much as 1.3Gbytes/sec for the 512Gbyte SSD board and 1.4Gbytes/sec for the 1Gbyte and 2Gbyte SSDs. Peak write speeds for the drives are 1 and 1.4Gbytes/second respectively and sustained write speeds are 550 and 950 Mbytes/sec respectively. The purpose of using PCIe interfaces rather than the industry standard SATA interface for SSD interconnect is to bypass the limitations built into the SATA interface standard and protocol due to the assumptions made about rotating memory that are baked into the SATA protocol. Instead of being limited to 1.5 or 3 Gbits/sec interface speeds and the protocol overhead incurred when dealing with rotating memory, an 8-lane PCIe interface supports bidirectional, simultaneous read and write transfer speeds of approaching 4 Gbytes/sec, about an order of magnitude faster than SATA. In fact, OCZ’s press release states: the “ Z-Drive R2 SSD maximizes bandwidth by taking the SATA bottleneck out of the equation and utilizes the speed advantages of the PCI-Express interface.“

The higher speed of the larger OCZ SSDs arises from the additional parallelism of the additional NAND Flash DIMMs added to the board to increase capacity. So it’s clear that OCZ has employed a Flash controller that understands and can exploit the additional parallelism provided by the extra NAND Flash DIMMs. A 1-million-hour MTBF suggests that the Z-Drive R2 SSD’s on-board controller is also carefully monitoring the health of the on-board NAND Flash and is performing appropriate wear leveling as well.

By Steve Leibson, Technology Evangelist, Denali Software

The recent, very successful launch of Apple’s iPad introduces both a new gadget and an entirely new product category to the consumer and business markets. Apple announced last Monday that it had sold more than 300,000 iPads on April 3, the first day that the iPad was available in the US. (That includes pre-orders, of course.) Note that this number tops the first-day sales of Apple’s iPhone. Analyst predictions are all over the map, projecting that Apple will sell somewhere between 4 and 7.1 million iPads in 2010 as the company starts to sell the product around the world. Each Apple iPad contains 16, 32, or 64 Gbytes of MLC NAND Flash depending on selected options. No wonder, therefore, that DRAMeXchange is predicting that the introduction of the iPad and copycat products from other vendors will have a stabilizing effect on NAND Flash pricing for the foreseeable future. There’s a built-in, assured demand for high-capacity NAND Flash chips in the middle term.

Last month, DRAMeXchange noted that mainstream MLC NAND Flash pricing had declined by a few percentage points over 1Q 2010 and that the market seemed to stabilize during the first half of March. Looking forward, DRAMeXchange expects MLC NAND Flash pricing to stabilize due to the demand by this new product category. In fact, iSuppli’s iPad sales estimate for next year is for nearly 15 million units sold and the company’s estimate for 2012 just crosses the 20 million/year threshold. Those numbers plus competing products in the new category suggest a rapidly growing and large market for high-capacity MLC NAND Flash devices.

Sources for the MLC NAND Flash used in Apple’s iPad have appeared in photos of the iPad teardowns conducted by the US FCC in February and by iFixit.com last weekend. The earlier FCC teardown concealed the vendor markings on the chips with gray rectangles but subsequent image processing of the FCC photos by Anandtech and iFixit.com using a little help from Photoshop revealed Toshiba NAND Flash ICs in the pre-production FCC teardown unit. The iFixit.com teardown on an as-sold, production iPad shows two of Samsung's K9LCG08U1M 64Gbit MLC NAND Flash memory chips soldered to the iPad’s processor board alongside the proprietary, Apple-designed A4 processor chip . iSuppli’s estimates in February placed a cost of between $29.50 and $118 on the 16 to 64 Gbytes of NAND Flash built into each iPad.

Guest Blogger: Marc Greenberg, Director, Technical Marketing

The day is finally here - DRAMExchange.com quoted that the session average price of 1Gbit DDR3-800 parts on April 2nd was $3.03 while 1Gbit DDR2-800 was $3.04.

Only DDR2 memory manufacturers will be celebrating... you should realize that this point has been reached because of rising prices on DDR2 to meet the DDR3 prices, not because of falling DDR3 prices. DDR3 has been holding relatively steady in the $2.50 to $3.00 per gigabit range over the last year, while DDR2 prices for 1Gbit have risen from around $1.00 a year ago to over $3.00 today.

Denali were originally projecting that the DDR2/DDR3 price crossover would happen sometime in 2009 and here it is in the second quarter of 2010. We have a pesky recession to blame for the delay - in the depths of the recession, some 512MBit DDR2 parts were sold for $0.35 and the DDR2 price remained depressed for longer than predicted. Thanks to the recovery, people are buying PCs again, and many are still using DDR2.

What does this mean for you?

Well, I should start by saying that this is the *first* price crossover. Prices tend to cross over 2-3 times during the lifetime of the product. As new DDR3 capacity comes on-line, DDR3 prices may drop. As new DDR3 products come on-line, prices may rise. As old DDR2 capacity is turned off, DDR2 prices may rise. As old DDR2 products are retired, DDR2 prices may drop.

For the near-term, if you are designing a product where the performance of DDR2 is sufficient, you should plan on supporting both DDR2 and DDR3 in your product to allow you to take advantage of whichever part is cheapest at the time of manufacture.

By Steve Leibson for Denali Software

The appearance of SSDs into the storage arena is rapidly altering the way large-scale, enterprise-class storage systems are built. Gartner Principal Analyst Sergis Mushell discussed some of these changes at the recent Storage Visions 2010 conference held in LasVegas. Mushell focused on how the introduction of SSDs into the enterprise-class storage device market was reshaping foundation concepts in terms of form factors and interfaces. Mushell started by discussing form factors and projected the graph in Figure 1, which forecasts unit sales of enterprise-class SSDs by form factor:

Figure 1: SSD distribution by form factor (Gartner)

The first thing to note about this graph is the unit-growth forecast for enterprise-class SSDs shown at the top of Figure 1, from 281,000 units in 2008 to 5.3M units in 2013. That’s a 20x increase over a 5-year period and that’s healthy growth is attracting new and existing storage vendors into the enterprise-class SSD market.

Next, notice the relatively rapid decline in the use of 3.5-inch, enterprise-class SSDs. Although these drives constituted the bulk of the enterprise SSD market in 2008, Mushell's chart predicts that 3.5-inch SSDs will become a mere sliver of the market in 2013. At the same time, shipments of 2.5-inch, enterprise-class SSDs appear to stabilize at approximately half of the market. The big percentage growth forecast is for board-mounted SSDs either as PCIe expansion cards or as plug-in DIMMs—not really drives at all.

These forecasts are consistent with three industry trends. First, the unrelenting application of Moore’s Law doubles NAND Flash capacity about every 18 months, so volumetric requirements for the same storage capacity shrink accordingly. Hence the decline of the relatively large 3.5-inch form factor. (Old-timers in the storage industry might crack a smile at the idea that 3.5-inch drives are “large.”)

Second, there’s no particularly good reason why SSDs should be packaged in form factors that are based on the requirements of mechanical rotating storage (hard disk drives, HDDs). Existing HDD form factors are artifacts of platter-size choices and the actual dimensions represent a logical physical progression from 8-inch and 5.25-inch HDDs down to 3.5- and 2.5-inch drives over several decades. Server designers often find these existing HDD form factors to be troublesome. SSDs can assume any convenient or odd form factor because they’re entirely electronic and made of ICs. They initially adopted HDD form factors to allow easy, drop-in replacement of existing HDDs but the use of HDD interfaces is really just another anachronism, as the rapid forecast growth of PCIe-based and DIMM-based SSDs suggests.

Which leads to the third trend and the next graph Mushell displayed, shown in Figure 2:

Figure 2: SSD distribution by interface (Gartner)

This graph forecasts market share for the enterprise-class SSD market by interface type. Note the dominance of Fibre Channel SSDs in 2008, which is consistent with a disk-replacement strategy. Fibre Channel has dominated enterprise-class storage thanks to its high transfer rates but that dominance is ending for both HDDs and SSDs as faster SAS and SATA interface standards appear. Figure 2 forecasts a rapid decline in shipments for SSDs with Fibre Channel interfaces, which predicts that the percentage of enterprise-class SSDs shipped with Fibre Channel interfaces will plummet from nearly 70% of all enterprise-class SSD shipments in 2008 to virtually nothing in 2013. According to this forecast, Fibre Channel’s reign washes away in three waves. The SATA (serial ATA) interface represents the first big challenger to Fibre Channel’s dominance, followed by SAS (serial attached SCSI), and finally by PCIe, which isn’t an HDD interface at all.

SAS and SATA HDD interfaces have been pressed into duty as SSD interfaces for at least two logical reasons. First, these interfaces have become dominant because of their widespread use for all HDD classes, not just the enterprise class, which means that the storage industry has developed a tremendous infrastructure to support these two HDD interfaces. That infrastructure includes everything from driver, OS, and database software; to drive testers; to cables, connectors, and built-in chipset support. In any market, broad infrastructure support and the correspondingly reduced implementation and support costs constitute powerful compatibility incentives that drive vendors cannot ignore.

Second, as HDD manufacturers enter the SSD fray either by developing their own SSD architectures and designs or by buying SSD vendors outright, the use of HDD interfaces on SSDs presents the appearance of a unified product line to customers. Left alone to their own world of storage, existing drive vendors with established HDD product lines have no strong need or wish to differentiate SSDs based on interface type and prefer to offer either type of storage to their customers as plug-compatible alternatives. Established drive vendors’ predisposition to support and maintain legacy HDD interfaces opens the door wide for new SSD vendors that do not have legacy HDD interfaces to support.

As discussed in a previous blog entry, it’s possible to develop SSD architectures that easily outperform HDD interfaces simply by increasing the number of parallel NAND Flash channels in use. It’s not possible to perform the same trick with HDDs. To get higher data rates from HDDs, manufacturers can:

• Spin the disks faster—but at 15,000 RPM, enterprise-class HDD platters are already under severe mechanical stress.
• Increase the number of read/write heads that can be active simultaneously—which constitutes a radical, substantial, and costly architectural and electronic change to HDD design.
• Add a second servo actuator with another set of read/write heads and another set of read/write electronics—which is completely out of the question from an economic perspective.

Consequently, some SSD vendors are beginning to use faster interface standards that are not constrained by disk-centric assumptions that have been baked into standard HDD interfaces including even the latest versions of SAS and SATA. PCIe is a good example of such an unconstrained interface. A 16-lane, Generation 2 PCIe interface provides 8 Gbytes/sec of throughput (much more than SAS or SATA) and a 16-lane, Generation 3 PCIe interface provides 16 Gbytes/sec of throughput. These substantial throughput rates underlie Gartner’s forecast for the eventual decline of all HDD form factors and HDD interfaces in SSD applications.

Related Information:

• Why the Solid State Drive Market is Poised for Growth
• Mr. NAND's Wild Ride: Warning — Surprises Ahead!
• Does MLC flash belong in enterprise SSDs?