A View from Christopher Mims
Seagate Demos First Hybrid Hard Drive
Performance is boosted by algorithm that caches frequently-used data.
Seagate’s hybrid drive. Credit: Seagate.
On Monday, Seagate released details of a new hybrid Flash memory-hard disk drive, which is intended to significantly boost performance of notebook computers.
The drives combine a traditional 250, 350 or 500 GB spinning platter drive (HDD) with 4 GB of single-level cell Flash memory, which is intended to be more reliable than cheaper varieties of flash memory. (Seagate says it has tested its SLC flash to levels reached after 5 years of use and found no degradation of performance or data loss.)
The result is a combined drive that approaches the performance of solid state drives, but at a fraction of the price. According to Seagate’s own tests, the Momentus XT is 80% faster than a traditional notebook hard drive, and 20% faster than an ultra high-performance 10,000 RPM HDD.
The speed boost is due almost entirely to the drive’s Adaptive Memory algorithm, which learns which applications and files a user accesses most, and dumps those in the 4 GB of flash memory. Flash has 150 times the access speed of a traditional hard drive, but only 2 times the read/write bandwidth.
The technique of balancing a cache of expensive flash memory, which is great at randomly accessing many small files, with a large hard drive, which is many times cheaper per gigabyte and is good at reading and writing large files, mirrors a similar approach currently being explored in the data center.
Two papers which appeared in 2009, Migrating enterprise storage to SSDs: analysis of tradeoffs, from Microsoft Research, and Gordon: Using Flash Memory to Build Fast, Power-efficient Clusters for Data-intensive Applications (pdf), from the Non-volatile Systems Laboratory at UC San Diego, map out a data center-scale version of the new drives from Seagate.
As most observers intuit, and the research from UCSD confirms, replacing traditional disk clusters with next-generation flash SSDs improves both overall performance and performance per watt. This is the same effect that’s seen in notebooks and netbooks that already rely on SSDs for fast boot times.
However, as the work from Microsoft Research revealed, at current prices for flash memory, replacing even just a portion of the solid state disks in a data center with flash SSDs is not cost-effective. The work asserts that flash SSDs would have to become between 3 and 3000 times as cheap to beat disks in the data center. And so it is with Seagate’s new drives, which, despite being merely hybrid drives, are currently around twice as expensive as comparable drives with the same capacity.
While Seagate’s drives borrow strategies explored research on the data center, it’s also unclear that the devices will be used in the data center anytime soon, where control over the behavior of individual components is of the utmost importance.
As storage guru Robin Harris put it, “don’t count on these showing up in RAID arrays soon. Arrays already have a lot of moving parts and hybrid drives add some subtle wrinkles.”
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