Hybrid Storage: Combining HDD and SSD Drive
The hard disk drive (HDD) has always been a traditional mainstay in the storage technology with annual growth of 40% in the capacity but with only 2%increase in its performance. This signifies that for enterprises may not fully depend on the HDDs for both high capacity and performance as it lack the capabilities to deliver a cost effective device technology. Due to this drawback, SSDs have gained prominence in the storage solutions industry which offers exceptionally high performance but much less capacity per drive. The cost of SSDs are also considered to be more expensive compared to HDDs and have a write endurance limit. considering the properties of both drives, one can come up with a cheaper and high performing drive through the hybrid storage option.
We can define a hybrid drive(also known as solid state hybrid drive) as a logical or physical storage device which is responsible for combining a faster storage medium such as solid-state disk drive(SSD) with a higher-capacity hard disk drive(HDD). The intention of the hybrid disk is adding some of the speed of SSDs to the cost-effective storage capacity of traditional HDDs the SSD works as a hybrid drive is to act as a cache for the data stored on the HDD, improving the overall performance by keeping copies of the most frequently used data on the faster SSD.
The two major hybrid storage technologies for combining NAND flash memory or SSDs, with the HDD technology are:
- dual-drive hybrid system
- solid-state hybrid drives.
Dual-drive Hybrid System
It combines the usage of separate SSD and HDD devices which are installed in the same computer. Overall performance of the storage optimizations are managed in following ways:
- One can manually places more frequently accessed data onto the faster drive.
- Through the computer’s operating systems, that combines SSD and HDD into a single hybrid volume, by providing an easier experience to the end-user.
- By chipsets external to the individual storage drives. An example is the use of flash cache modules(FCMs). FCMs combine the use of separate SSD and HDD components, while managing performance optimizations.
Solid-state hybrid drive
It refers to products that incorporate a significant amount of NAND flash memory into a hard disk drive(HDD), resulting in a single, integrated device. The purpose behind SSHDs is to identify data elements that are most directly associated with performance (frequently accessed data, boot data, etc.) and store these data elements in the NAND flash memory. This has been shown to be effective in delivering significantly improved performance over the standard HDD.
Anatomy of the Hybrid Hard disk drive
Working of a SSHD
SSHD technology works by using a relatively small amount of high-performance NAND flash solid state memory to store the most frequently used data. This is the SSD portion of the drive, typically around 8GB in size, meaning files can be accessed far quicker than HDD.
The rest of the SSHD is made up of traditional HDD storage, usually 1TB and above, to hold the bulk of your lesser used files. This could be anything from games to video music and documents.
Since an average computer workload accesses a relatively small portion of the entire data stored, most frequently used data needed by the host computer will be located in the solid state memory when requested.
When this is the case, system performance improves because there is less time spent locating, reading and delivering data to the computer.
Operation
The goal of hybrid storage is to combine HDD and a faster technology (often NAND flash memory) so as to provide a balance of improved performance and high-capacity storage availability. This is achieved by placing hot data, or data that is most directly associated with improved performance, on the faster part of the storage architecture.
The core of SSHD technology decides which data elements are prioritized for NAND flash memory .
Modes of operation
Self-optimized mode: The SSHD works independently from the host operating system or host device drives to make all decisions related to identifying data that will be stored in NAND flash memory. This mode results in a storage product that appears and operates to a host system exactly as a traditional hard drive would.
Host-optimized mode (or host-hinted mode):In this mode of operation, the SSHD enables an extended set of SATA commands defined in the so-called Hybrid Information feature, introduced in version 3.2 of the Serial ATA International Organization(SATA-IO) standards for the SATA interface. Using these SATA commands, decisions about which data elements are placed in the NAND flash memory come from the host operating system, device drivers, file systems, or a combination of these host-level components. Some of the specific features of SSHD drives, such as the host-hinted mode, require software support from the operating system. Microsoft added support for the host-hinted operation into windows 8.1, while patches for the Linux Kernel are available since October 2014.
References:
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