Clever new packaging for DRAM memory chips will help to accelerate server performance to striking new levels, and make SSD a better buy, too.
Everyone knows that DRAM, the stuff they make server main memory from, runs fast: nanosecond access times, transfer rates of around 12GBp/s. So, when system performance is of the essence, why not just cache lots of data in main memory and be done with it? After all, many modern servers can easily handle 500GB of RAM or more.
In fact, for some applications, this approach may make sense. Even desktop computers have long been able to create so-called RAM drives.
The problem is that on a per-bit basis, DRAM costs a fair amount, and worse, it is volatile. No power, no data retention, which means that in many applications, there's always the risk that a power outage will wipe out any valuable information residing in RAM.
This situation promises to change in coming months, however, as something called the non-volatile DIMM (for dual-inline memory module) hits the market in volume. These are memory sticks that include their own electrical supplies -- just enough power to retain data until regular power is restored.
These new sticks will get this electricity from what are called ultra-capacitors. Souped-up versions of the capacitors used in radios and other circuits, they are able to hold power at a higher density than batteries. They also have a longer useful life -- five, seven, even 10 years -- and they don't require conditioning when first put into use. (In fact, ultra-capacitors may eventually power cars, but that's another story.)
Now, don't get any ideas. This new form of DRAM is not about to obsolete SSD, whose flash memory chips perform much more slowly. NV-DIMMS will, however, help customers get a better ROI from any SSD they install by reducing the wear and tear on those somewhat fragile devices.
At least, that's what Adrian Proctor tells me. He's vice president of marketing at Viking Technology, one of several companies gearing up to ship NV-DIMMs in quantity. The parts will start showing up early next year, Proctor says, in servers supplied by major manufacturers such as HP, IBM, Dell, and Oracle, and in certain storage systems, as well. The sticks require a modified BIOS in the server, which means end-users won't be able to add them as they like to any old server. VARs, though, will be able to help.
How this memory will help SSD, Proctor explains thusly:
Flash memory, it's widely acknowledged, has an issue with write cycles. Put simply, the more times data gets written to a chunk of flash, the more chance there is that some number of its millions of memory cells will lose their ability to retain data, and the slower the memory will perform overall. Intensive Write activity over the course of two or three years can diminish data retention from six months to a mere couple of weeks.
This is true for SSD in the datacenter and for the memory card in your camera. System-level techniques have been developed to work around these accumulative failures, but the issue is only getting more troublesome as flash memory cells shrink with every manufacturing generation.
Need for speed
The new NV-DIMM memory stands to help, Proctor asserts, by offloading much Write-intensive work from SSD and thereby extending SSD's useful life. As it is, to overcome the inevitable erosion of flash performance, customers over-provision SSD and manufacturers resort to involved error-correction techniques, and that effectively jacks up the cost of SSD.
NV-DIMMs will certainly cost more than comparable DRAM, though just how much, Proctor declines to specify. Viking, he notes, is selling through OEMs and will let them set prices. Some applications, he notes, will enjoy a major speed-up from simply having, say, 48GB of DRAM cache on hand. Other apps will be able to factor in the extended ROI from SSD, as well.
Either way, it looks as if yet another form of memory is on its way into the datacenter, promising to accelerate performance and give managers more options to choose from.
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