WD Intros 'World's Thinnest' 2.5-inch Hybrid Hard Drive
Western Digital is now sampling 5-mm hybrid drives to OEMs.
Western Digital (WD) said on Monday that it's currently sampling 5mm-thin hybrid hard disk drives designed to fit within super-thin notebooks (AKA Ultrabooks, etc). These new drives promise SSD-like instant-on and application performance on top of the typical high capacity and low price point traits offered by traditional HDD.
"Mobile devices are becoming smaller, thinner, lighter and more responsive," said Matt Rutledge, vice president of client storage solutions at WD. "Working with our technology partners, WD has developed new 5 mm hard drives that enable high capacity storage along with excellent performance and superior economics to allow our customers to expand their thin offerings."
WD's hybrid tech contains two components: MLC NAND flash storage for SSD-like data throughput and instant-on responsiveness, and magnetic disks for efficient, high-capacity storage. The combined tech will manage data in tiers, throwing the "hot", highly-used data onto the NAND flash chips and the less-used "cold" data on the silver platters.
"The tiered design of hybrid hard drives, compared to current dual-drive solutions, also provides a redundancy benefit for users," WD said. "The magnetic disk backs up all files residing in the NAND, protecting the user from inevitable NAND wear and preserving it for the more hot data handling. WD’s hybrid technology works in conjunction with the PC operating system to deliver higher performance than current hybrid offerings while minimizing NAND wear to allow the use of less expensive MLC NAND."
Unlike other hybrid solutions, WD claims that its new drives provide a single-unit design. Even more, they're smaller than the super-thin 7-mm HDDs WD's began shipping for Ultrabooks and other super-thin notebooks earlier this year. In comparison, 2.5-inch HDDs typically measure 9.5-mm, thus the new hybrids utilize almost 50-percent less volume.
WD said the new drives will be showcased during WD’s Investor Day, Sept. 13, 2012.

They're probably fine... However, I make no guarantee about that claim, at least not yet.
Rotation speeds won't be too much of a factor with the cache, but I doubt it will be less than the current standards.
The reason more info isn't available is for IP reasons. That's pretty obvious.
The Seagate hybrids were a good start, they don't have a lot of cache but it is SLC. They also have the advantage of being completely software-agnostic. But caching systems that depend on a certain OS/software combo have some advantages too. Look at the caching system Intel uses. If WD does something like that, only without the need for a seperate cache drive, they might be on to something. I'm assuming they're using lots of spare area, and it looks like they're not caching writes or something, because they claim redundancy. So even if the MLC suffers lots of failures, you don't lose your data.
And SSD makers: It is OK to not have the 'fastest' drives available. There is a huge market out there for people who just want cheap, reliable, low power storage in the 250-500GB range. For these people speed is a nice perk, but the low .1ms access time, and the low power are way more important. 200MB/s is plenty fast to keep a mobile CPU busy, and anything much faster than that is just wasted power. Lastly, make it reliable so that we do not have to fear digging into the bowels of our mobile devices every year when a drive fails.
Just focus on $/GB, power savings, and reliability and you will get a whole host of buyers who either don't care about the extra speed, or who have hardware (read Atom, Celeron, Pentium, and i3's) that cannot take advantage of that extra speed.
If small and thin is so important, why not just use 1.8" drives ?
So give it a chance before swinging down the gavel on them.
Someone hasn't looked at any modern benchmarks on good hybrid drives.