Category: DAS

In part 1 (see previous post here), we discussed the underlying technology for SanDisk‘s UltraDIMMs based on Diablo Technologies MCS hardware and software. IBM will be shipping UltraDIMMs in their high end servers later this year as their new eXFlash.

In this segment we will discuss what SanDisk has put on top of the Diablo Technology’s MCS to supply SSD storage.

SanDisk UltraDIMM SSD storage

In the UltraDIMM package, SanDisk supports 200 or 400GB of 19nm MLC NAND SSD storage that is accessed via SATA [corrected after this went out, Ed.] internally, but the main interface is the 1600MHz, DDR3 to the UltraDIMMs.  As each UltraDIMM card plugs into any DDR3 memory slot you can potentially support multiples of these cards in a single server. I believe the maximum number is 7 UltraDIMMs, not sure if IBM supports this many [corrected after this went out, Ed.] dependent on the number of memory slots in your server. IBM on their x3850 and x3950 can support up to 32 UltraDIMMs per server.

SanDisk uses their Guardian Technology to enhance NAND endurance beyond what’s possible with native NAND controllers. One of the things that Guardian Technology does is to vary the voltage used to program the NAND bits over the life of the bit cells/pages. So early on when the cell is fresh, they can use less voltage and as it ages they increase the voltage to insure that the bits are properly programmed. With other NAND controllers, using the same voltage across the whole NAND lifetime it will unduly stress the NAND bits early on and later as they age, it will be unable to program properly and will need to be flagged as bad.  The NAND chips/bits are characterized so that SanDisk Guardian Technology can use an optimum voltage curve over the chips lifetime.

The UltraDIMMs also have powerloss protection. This means that any write to an UltraDIMM memory that’s been acknowledged to the server is guaranteed to have sufficient power to make it all the way to the SSD storage.

Another thing that MCS memory interface brings to the picture is Error Correction Circuitry (ECC). Data written to UltraDIMMs has ECC protection throughout the data path up from the server DRAM memory, through the DIMM socket, all the way to the SSD flash.

As discussed extensively in Part 1 of this post, access times for UltraDIMM storage is on the order 7µsec, which is ~7X faster than best of class PCIe Flash storage and a single UltraDIMM card is capable of sustaining 20GB/second of data throughput. I know of enterprise class storage systems that can’t do half that in throughput.

On the other hand, one problem with UltraDIMM storage is that they are not hot swappable. This is primarily a memory interface problem and not an UltraDIMM issue but nonetheless, you can’t swap an UltraDIMM module until the server is powered down. And who would want to do such a thing when the server is powered anyway?

SanDisk long history in NAND

As you can see from the three photos at right SanDisk seems to have been involved in flash/NAND technology innovation since the early 1990’s.  At the time NOR and NAND were competing for almost the same market.

But sometime in the mid to late 1990’s NAND found a niche in consumer cameras and never looked back. Not sure where NOR marketis today but it’s a drop in the bucket compared to the NAND market

UltraDIMMs is just the latest platform to support NAND storage access.  It happens to be one with blazingly fast access times and high IO parallelism, but in the end it just represents another way to obtain the benefits of NAND for IT customers.

Also, SanDisk’s commercial NAND (Memory Card) business seems to be very healthy. What with higher resolution photos/video/audio coming online over the next decade or so it doesn’t seem to be going away anytime soon.

SanDisk is in a new joint venture (JV) with Toshiba to produce 3D NAND flash. But in the mean time they are still using 2D flash for their current SSD storage. Toshiba and SanDisk in their current JV together manufacture about 1/2 the NAND bits in the world today.

The rest of SanDisk NAND business also seem to be doing well. And the aforementioned JV with Toshiba on 3D NAND looks positioned to take all of this NAND to the next level of density as well which should make all of us happy.

SanDisk acquiring FusionIO

SanDisk was in the news lately as they have recently filed to acquire FusionIO, a prominent and early PCIe flash supplier that in recent years has broadened their portfolio to include enterprise storage with their acquisition of NexGen storage (renamed IO Control).

When FusionIO IPO’d the stock sold at ~$19/share and SanDisk is purchasing the company in an all cash deal for $11.25/share almost a 40% reduction in share price in 3 years (June’11 IPO) – ouch.  At IPO the company was valued at ~$2B, (some pundits said this was ~$1.5B, so there’s some debate on the original valuation). SanDisk is buying the company for ~$1.1B in cash. Any way you look at it, they paid significantly less than what the company was worth at IPO. Granted, it was valued at 41X earnings then and its recent stock price at $11.59 represents a 3.3P/E (ttm).

Not exactly certain what happened. Analysts seem to indicate that Apple and Facebook, FusionIO’s biggest customers were buying less FusionIO product. I also happen to think that the PCIe flash space has gotten pretty crowded over the last 3 years with entrants from Micron Technologies, Intel, LSI, Verident/Western Digital, and others.

In addition, for PCIe flash to broaden its market there’s a serious need to surround it with sophisticated caching software to enable a more general purpose IO solution (see Pernix Data, Proximal Data, and others). These general purpose, caching solutions have finally reached high levels of sophistication and just now are becoming more widely available.

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Originally, part 3 of this series was going to be on IBM’s release of the UltraDIMM technology  as their new eXFlash. However, I am somewhat surprised not to see other vendors taking up the MCS/UltraDIMM technology but IBM may have a limited exclusivity to it.

The only other thing thats this interesting happening in solid state storage is HP’s Memristor Machine which is still a ways off.

Nonetheless, a new much faster memory card based SSD is hitting the market and if history is any indication, it won’t be long until the data storage world will sit up and take notice.

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