Hybrid hard drives: a technology of the future?

Introduction

In 2007, Seagate and Samsung demonstrated drives hybrids, a compromise between the magnetic hard drives and SSDs, where a regular magnetic drive is combined with a large cache of flash memory and made a special firmware able to take advantage of it to speed up read operations and (in some cases) also recording. In theory, hybrid drives offer some interesting advantages with respect to both regular and hard drives to SSDs, as they offer lower access times for frequently accessed data (especially operating system components) and do not have the problems that affect the reliability of SSDs cheaper (based on MLC chips), since the cache is always based on SLC chips, which have a greater durability. Also, being in essence enhanced magnetic hard drives, they also soften the very issue of cost, since they can have multiple terabytes of capacity without costing an eye and a kidney as in the case of SSDs.

The major problem with hybrid hard drives was that the initial generation of drives was impaired by the use of slow flash memory chips and firmware problems, which ended up causing the performance gain compared to magnetic hard drives were too small to justify difference in cost. In short, all HD has a small cache of RAM, which although small capacity, is very fast, providing significant gains in many operations. Flash memory chips are much slower, so that in many situations the small cache of RAM found in regular hard drives offer more tangible gains that a large cache of flash memory.

Another problem was the adoption of SSD Caching by Intel, which overshadowed the hybrid hard drives, offering a solution very similar from a practical standpoint. Instead of paying more for a hybrid HD, you could afford a small SSD, which would be automatically used by the Z68 chipset (and successors) as an intelligent cache, storing 20, 40 or 64 GB of frequently accessed data.

Intel invested heavily in both the chipset and optimizations in the firmware (even created a family of SSDs optimized for the task), which resulted in tangible gains in performance. At the opening of applications and games, for example, the system ends up offering from Intel similar results to those of an SSD, but on the other hand gains are inconsistent, varying according to the frequency and order in which applications are open, as reported by Anand.

Despite the setbacks, the Seagate insisted on the segment, recently launched the third generation of hybrid hard drives, as the Seagate 750 GB Momentus XT:

He is a drive of 2.5 ", aimed for use in notebooks, which combines a magnetic drive 750 GB with 8 GB of cache, faster chips based on SLC flash memory that Seagate could find. In short, is a smaller capacity than you would when using the Intel SSD caching, but with greater flexibility, since the Momentus XT can be installed on any system, regardless of the setting or chipset used. Every cache management is done by the drive, dispensing any special support by the operating system.

Although a 2.5 drive, the platters spin at 7200 RPM, ensuring right from the beginning a performance far superior to most of the drives of 2.5 ", which use much lower speeds. Seagate also improved the intelligence of the firmware in relation to drives with 500 GB and 4 GB of cache the previous generation, making the drive smarter about what should or should not be stored in the cache, taking into account the frequency with which files are accessed, size and access latency.

Although the fact of being volatile flash memory offers a certain calm about the potential loss of data, Seagate chose to initially use the cache read-only, so that even if some of the flash memory chip cache fail at some point , there is no risk of data loss. Support for use of the cache also for recording was promised by Seagate for the next month through a firmware update, but even that promise is fulfilled you have to manually update the drive to take advantage of the resource. Since most users even know that hard drives also need firmware updates, the update will go unnoticed to most.

In terms of performance, the Momentus XT is quite interesting, offering very similar to the gains offered by the Intel SSD caching. These figures show ExtremeTech an ideal scenario, where the loading time of applications is very close to the one offered by SSD:

The main problem is that the performance gain comes with a cost assalgamento with the Momentus XT coming to market by no less than $ 245, a price comparable to many 256 GB SSDs. In short, you have three times the capacity, in exchange for a much higher power consumption and performance much more inconsistent.

The conclusion is that the Momentus XT remains the central problem of earlier generations of hybrid drives, which is the fact of being halfway between the low cost of hard drives and magnetic performance of SSDs in a market that is increasingly polarized between the two extremes. The price increase of magnetic drives caused by floods in Taiwan can benefit a little by Seagate, reducing the difference between the Momentus XT and regular magnetic competitors, making the company chooses to keep the show going, but the long-term technology tends to be abandoned in favor of systems based on chip cache and the use of SSDs.

This explains the fact that only Seagate is investing in technology, and even then only in a series of hard drives, compared to the dozens of different manufacturers that are investing in the production of SSDs.