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Unfortunately, the NAND for the Momentus XT is on the other side  (Source: Seagate)
Complete redesign combines speed with affordability

The promise of superfast access speeds has been fulfilled by solid state drives using NAND flash memory, but it comes at a high monetary cost. Many enthusiasts, prosumers, and corporate users have already adopted SSDs as hard drives are typically the primary bottlenecks in a computer system. While CPUs and RAM measure their access speeds in nanoseconds, traditional magnetic-based hard disk drives are still measured in milliseconds.

The primary advantage for HDDs is the low cost of production, even for faster 7200 and 10k RPM drives. Samsung and Seagate tried before to bridge the gap between low-cost HDDs and fast SSDs using a hybrid hard drive, combining a single magnetic platter with a small amount of NAND flash memory. The NAND would act as a cache, similar in theory to a small scale tiered storage solution like that used by many corporations for their datacenters.

However, the experiment failed. NAND was still too expensive in 2007, and the small amount that was used proved insufficient. Performance turned out to be worse in some situations, and the capacity of Seagate's sole model was soon overtaken by other products with higher areal density.

Now, three years later, Seagate has learned its lesson with its all new Momentus XT. The company calls it a Solid State Hybrid Drive, and it will be available exclusively in a 2.5-inch form factor. There are 250, 320, and 500GB models, all of which feature 32MB of DRAM cache and a 4GB single-layer cell NAND flash cache. There will unfortunately not be any 6Gbps SATA support, despite the XT moniker.

The secret sauce this time is what Seagate calls "Adaptive Memory". The firm has developed new algorithms based on their years of research and producing firmware for regular drives. These algorithms monitor data access transactions over time, and will place a copy of the most frequently accessed data (such as Windows system files) onto flash storage. A table also keeps track and counts of how frequently data is used in order to prioritize it for retention and caching.

This is similar in concept to Microsoft's ReadyBoost, but uses much faster SLC rather than the sluggish commodity NAND that ended up being used in USB flash drives and SD cards. The algorithms are also much more advanced, as is the garbage collection and firmware. Seagate developed its own proprietary NAND flash controller specifically for the Momentus XT.

This also means that the Momentus XT is also operating system agnostic, and can be used with Unix/Linux environments and MacBooks.

Seagate insisted on using the flash as a cache instead of primary storage for additional reliability. Their tests show that over 250GB of data a day could be written to the NAND for 5 years and it would still function.

Although the Momentus XT isn't as fast as an SSD, Seagate thinks that it will be close enough that its customers won't be able to notice the difference qualitatively. While most consumers will notice the difference between a 5400RPM drive and a 7200RPM drive, they might not necessarily notice the difference between a 7200RPM and 10k RPM drive, an argument that the company has used before as a justification for not producing a 10k RPM consumer drive.

To continue the example, Seagate likens the Momentus XT to a 7200RPM drive and SSDs as 10k RPM drives; while the SSDs are much faster, qualitatively consumers won't notice the difference. The company expects that it will be able to hold off the SSD onslaught for a couple of years with this strategy, despite the lowering cost of NAND flash memory. In fact, as NAND flash prices drop due to the introduction of new process nodes, Seagate will be able to fit more NAND into the same space and offer even greater performance.

The first OEM to adopt the Momentus XT will be ASUS for their ROG G73JH gaming laptop, which will feature two of the drives. Seagate will also be shipping Momentus XT drives out to the channel this week for retail distribution.

Two reviews of the new Momentus XT can be found here and here.

Momentus XT








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RE: Hybrid drive
By therealnickdanger on 5/24/2010 10:09:59 AM , Rating: -1
That's not the only thing that's dead. Reviews are going up all over and this thing is pretty disappointing. Higher power draw, higher price, and lower performance than other 500GB HDDs. I'd chalk this thing up as a FAIL.

RE: Hybrid drive
By corduroygt on 5/24/2010 11:17:26 AM , Rating: 2
Which tests are those, AnandTech tests shows that it's considerably faster than a standard notebook drive. The power consumption is also in line with other 7200 rpm notebook drives as well. It's no SSD, but it's not priced like one either, so I think it's a nice bridge between SSD's and regular HDD's in a laptop. I personally go with an SSD, but I'd recommend this to anyone who doesn't want to shell out for an SSD in their laptop.

RE: Hybrid drive
By xsilver on 5/24/2010 11:32:18 AM , Rating: 5
Im also interested to know why regular drives havent ramped up the amount of cache included. I mean even a 3.5" drive only has 64mb? Is that kind of density even value for money anymore? I would have thought you could get 128mb/256mb chips as a sweet spot (only extra $2/5) At least something like the caviar blacks or raptors should have at least this much cache.

RE: Hybrid drive
By therealnickdanger on 5/24/2010 12:20:07 PM , Rating: 2
Hmm, AT's review wasn't up earlier this morning. That does change things a bit. I had only seen Tom's and Legit and I wasn't wowed by those. AT's review shows better performance than the other drives, but certainly confirms the higher power requirements (50% more at idle!). That's not so great for a notebook hard drive.

I dunno, I'm still not all that impressed. The price really needs to come down. At $150, that's nearly 3x the price of a regular 500GB laptop drive. 500GB for under $100 would be sweet, but only for a notebook. For the desktop, I'll stick with my speedy SSD + HDD combo. Like Anand said, it would be nice to see what a real hybrid hard drive (read AND write) is capable of.

RE: Hybrid drive
By corduroygt on 5/24/10, Rating: 0
RE: Hybrid drive
By Starcub on 5/24/2010 2:53:07 PM , Rating: 2
The higher power draw can be explained by the difference in rotational velocity. The comparison drive uses only 5krpm platters, but the hybrid drive uses 7krpm platters. In a true comparison, the hybrid drive would likely draw less power since as Anand said, reads from the NAND cache draw significantly less power. Thus exactly how much less power the hybrid drive would drive in actual use would depend on the useage scenario.

You also have to compare the price of the hybrid to a comparable HDD. You can find 500GB 7k 2.5 drives for about $90 now. That makes the price difference between hybrid and normal HDD's equivalent to about what you would pay for a Robson module. The tech the hybrid drive uses is similar to that used by Robson. So the hybrid would be a good option for those that don't have a Robson module in their laptops. As the Anandtech tests show, you get most of the benefits of an SSD without having to pay SSD prices.

RE: Hybrid drive
By callmeroy on 5/24/2010 12:39:02 PM , Rating: 2
Your post and the one directly beneath it seem to be stark contradictions to one another.

If you read "reviews ....all over" about this being disappointing, care to post the links for clarity's sake?

RE: Hybrid drive
By Uncle on 5/24/2010 2:14:13 PM , Rating: 2
How about the sites that are paid by the competition through advertisement.. Isn't it normal to debunk your competition with erroneous negative reviews. One has to always read between the lines of any reviews even when it comes out of the horses mouth.

"The Space Elevator will be built about 50 years after everyone stops laughing" -- Sir Arthur C. Clarke

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