An Inside Look at the Hybrid Drive

Wednesday, February 25, 2015 by Jennifer Duits

For the past decade or so, solid state drives (SSDs) have been building popularity in the IT world. First, they infiltrated laptops and mobile devices with their small form factor and the void of moving parts. Now they are making their way into enterprise storage. Using the same flash memory found in USB drives, mobile phones and SD cards, and they offer a long list of benefits against their electromechanical HDD counterparts: they have no moving parts, are more resistant to impact and other forms of physical damage, and are blazing fast.

HDD storage capacities have increased pretty consistently - nowadays, massive 3TB and 4TB drives are now in the affordable range, and even 8TB and 10TB behemoths are making their way into the enterprise market. HDDs have hit a max of 15,000 revolutions per minute and are noisier, hotter, and require more power than their flash-based counterparts.

So, why haven't we all discarded our HDDs and switched to SSDs instead? Simple - cost per gigabyte, SSDs are more expensive. As of January 2015, a 1 TB HDD is under $50, where the equivalent SSD costs around the $380-$400.

In 2010, a number of manufactures, starting with Seagate and Samsung, began introducing a third choice in the world of drives in an attempt to bridge the pricing and performance gap between HDDs and SSDs…the hybrid drive. Since then, others like Western Digital and Toshiba have started making hybrid drives. The hybrid drive delivers some of the best features of both technologies by marrying the speed of an SSD with the cost-effectiveness of an electromechanical HDD.

How a hybrid drive works

The basics of a hybrid drive are to combine cache with the rotating electromagnetic platters of a HDD. A solid state hybrid drive (SSHD) usually has 8, 16 or 32GB of flash capacity and a larger HDD to store the bulk of the data. The idea is “hot data”, which needs to be quickly or frequently (i.e. an operating system or Outlook files) accessible, can be cached on the SSD and retrieved more quickly than if it were stored on the platters themselves. It's the same principle as installing both an HDD and an SSD on a desktop, aka a dual drive hybrid solution, except the performance optimization is built into the firmware and adapts to the storage needs. These adaptive or self-learning methods of optimization remove the need to manually move files/applications to the appropriate drive.

There currently are two modes of operation for all SSHD. The first is the self-optimization mode, or self-pinning mode, which designates devices that determine hot and cold data themselves. To the host machine, the drive appears no different to a traditional internal storage device.

The other SSHD mode is a host-optimization mode, or host-pinning mode. In this format, the host machine designates which data is hot and cold via its operating system, device drivers, and on occasion, other software.  The host machine sends designations to the drive via a regular SATA interface and instructs the drive how to store the data.

The advantages of hybrid storage

The key advantage of using a hybrid storage device is performance enhancement with high storage capacities, without a significantly larger cost (around $100 for a 1TB SSHD) while retaining high capacities. SSHDs have the storage capacity of an HDD, the increased retrieval speed for cached data over an HDD, but are not as expensive as an SSD of equal capacity.

Besides this, and faster access to critical data, there are other benefits to using SSHDs. For example, if calibrated correctly, you can  reduce stress and wear on the drive leading to a longer life expectancy than a traditional HDD..

... And the disadvantages

Although, hybrid drives are a great solution, they are not perfect. Data retrieval from the hard disk is just as fast as a traditional HDD. Hybrid drives are still as vulnerable to physical damage as a HDD and you do not benefit from the silence of an SSD. Being we are a data recovery company, we should discuss the data recovery implications of hybrid storage. The good news is being the solid state portion of a SSHD is used mainly as a cache or to store the operating system, you are unlikely to lose data from that portion of the drive. If you do manage to lose data from the solid state, the recovery presents its own challenges such as proprietary methods of data organization.

All in all, hybrid storage has plenty to offer to consumers and business users seeking the speed of an SSD at the same time as the attractive cost per gigabyte of an HDD. It is a great way to bridge the gap between HDD and SSD.