Hard disc drive (HDD) shipments are forecast to increase with total shipments reaching 575.1M units by 2016, according to IHS iSuppli market research firm. Undoubtedly, hard drive technology has progressed by leaps and bounds over the years, consistently increasing capacities and achieving high performance from today’s advanced microprocessors. With computer processing power doubling every two years, however, users have increasingly adopted solid state drives (SSD) to achieve faster performance and take full advantage of modern microprocessor technology.
And yet, the supposedly speedy performance of SSDs is dimmed by their associated expense and limited capacities in comparison to HDDs. Thanks to the emergence of solid state hybrid drives (SSHD), consumers can now achieve optimised performance and high capacity with a single device.
SSHD Technology and Other Hybrid Drive Solutions
SSHD technology represents the newest way to unify hard drive capacity and solid state performance. An SSHD combines solid state memory, like that used in an SSD, with traditional rotating memory found in an HDD. By integrating a small, affordable amount of solid state, or NAND flash, into the core architecture of a hard drive, SSHDs provide the performance benefits of an SSD, the storage capacity of an HDD and a price just slightly higher than that of a traditional drive. SSHDs are up to 4.5 times faster than comparable 7,200-RPM hard drives, with much higher capacities than those available on SSDs.
In the past, additional hybrid drive solutions have involved non-integrated combinations of SSDs and HDDs into a single computer system. These systems are controlled in a number of ways.
Dual-Drive Hybrid Solutions use separate SSD and HDD devices, which are installed in a single laptop or desktop computer. Host software manages overall performance optimisation of these systems. Apple Computer’s Fusion Drive is one example of a dual-drive hybrid solution.
Flash Cache Modules (FCMs) also combine separate SSD and HDD components and manage performance optimisation using host software, device drivers or a combination of both. FCMs are most commonly used with Intel Smart Response Technology (SRT). Specific Intel chipsets, in co-ordination with Intel storage drivers, implement SRT within the system. Most FCMs are used in the laptop computer market.
In each of these hybrid drive categories, the balance of improved performance and high-capacity storage availability is achieved by placing hot data, or data that is most directly associated with improved performance, in the NAND flash or SSD part of the storage architecture. Therefore, a mechanism must be in place to efficiently handle hot data. For Seagate® SSHDs, Adaptive Memory™ technology serves as this mechanism.
Adaptive Memory Technology
When Seagate introduced SSHD technology, the company created a set of advanced algorithms to track data usage and prioritise frequently used data for storage in the fast, solid state portion of the device. These algorithms, which form the basis of Adaptive Memory technology, were designed to change data priorities as different applications requested new data over time.
Implemented inside of the Seagate SSHD via firmware, Adaptive Memory technology is also referred to as self-learning technology. This is because the SSHD makes intelligent determinations about which data to store in NAND flash memory, without any influence from the host or related storage device drivers. Adaptive Memory technology works by identifying data elements that are important for enhanced host-level performance and promoting such data elements from HDD storage to NAND flash memory.
Because it works entirely within the drive, Adaptive Memory technology has first-hand knowledge of the data elements that are best handled by solid state memory versus traditional HDD storage, and can promote data to NAND flash memory based on this knowledge. For example, data elements associated with booting, restarting and hibernating a computer, in addition to other frequently requested data, are prioritised for storage in solid state memory. However, data elements associated with long, sequential data strings, such as in video or audio data files, do not benefit from being stored in NAND flash.
The Benefits of SSHD’s Integrated Architecture
As previously mentioned, the use of Intel Smart Response Technology (SRT) within Flash Cache Modules (FCMs) provides another way of joining SSD and HDD technologies to improve performance and preserve high capacity. While SRT will soon be commercially available with Seagate SSHD products using a new extension of the SATA I/O command set, current systems with SRT are implemented using separate HDD and SSD components.
To implement SRT in an FCM, specific Intel microprocessor and interface chipsets are used to configure the separate SSD and HDD components in a RAID configuration. All communication between the coupled devices is managed through the SATA interface.
In contrast, an SSHD’s integrated design enables all communication between the NAND flash and HDD media to be managed independently from the host system (Figure 1). This integrated design has several distinct advantages over an FCM:
Integration and Deployment: Because SSHDs are designed around standard HDD form factors, they are more easily integrated into a system and do not demand additional space. Deployment of SSHDs is also a breeze, as they function exactly like a typical HDD.
Cost: With fewer connectors and the elimination of certain components, SSHD designs are also lower in total cost than FCMs.
Data Integrity: SSHDs provide less risk of data separation. As FCMs use the SATA interface to move data between the individual SSD and HDD devices, the separation of data storage heightens the risk of data loss during power failure or device failure scenarios.
SSHD and NAND Flash – How Much Is Enough?
A common concern among potential users of SSHDs relates to the relatively small amount of NAND flash deployed in the devices. Seagate uses 8GB of NAND flash as the performance cache at the heart of the technology. Adaptive Memory technology is the brains of the system that chooses which data to store in this relatively small amount of flash.
Therefore, the key question becomes: is 8GB of NAND flash enough to meet the needs of end users and computer manufacturers? For the majority of computer users, the answer to this question is a resounding yes, as most computer workloads rely on a relatively small amount of the total data stored to achieve performance. This is a key concept behind all forms of hybrid storage and is explained by the fact that common personal computer applications—word processing, email, spreadsheets and many other client- or cloud-based applications—do not depend on large or frequently changing data sets.
There are, of course, exceptions to this rule. High-definition video editing and computer-aided design are two types of computer applications that use large, rapidly changing data sets. Such applications would not derive significant benefits from the use of SSHD technology.
Ever-improving microprocessor technology continues to push market demand for improved storage performance, and storage capacity demand continues to increase at over 50% every year. While SSDs have gained momentum in the storage market, they do not offer the cost effectiveness and capacity benefits of traditional hard drives.
SSHD technology is helping to meet the need for fast, high-density and reliable storage solutions. Using Adaptive Memory technology to make the most of NAND flash memory and HDD storage, SSHDs offer an ideal blend of speed and capacity. Now adopted by all major HDD manufacturers, SSHDs will continue to offer a compelling balance of performance, capacity and price.