Solid-state hybrid drive

A Solid-State Hybrid Drive (sometimes called simply a "Hybrid Drive") is a non-volatile digital storage device sometimes used in computers. It is essentially a combination of a hard disk drive and a solid-state drive. It is designed to offer speed, but also be inexpensive. These devices were first introduced by Seagate, and Samsung soon followed suit by releasing a similar product.

How it works

Since hard disk drives and solid-state drives have strengths and weaknesses, manufacturers have attempted to put these two together to offer the best of both. A solid-state drive is best for speed, since the flash memory therein has a much higher transfer rate (throughput) overall. However, flash memory is expensive, which means that sold-state drives are as well.
Hard disk drives have the clear advantage in this area, since they are much less expensive than solid-state, but they have a slower read/write rate. They are also durable, and do not typically wear out from being written to in excess. Although they have moving parts (the spinning platters and read arms), they tend to last very well.
Therefore, in Solid-State Hybrid Drives, a large amount of space is consumed by hard disk platters (usually 2.5 inch) and read arms with heads, but some space is also used by flash memory chips. When this drive is in use, cache data and important systems files are saved to the flash memory. The drive will also determine what other files are in high demand, and keep those on flash memory. The rest of the information which is used much less is stored on the hard disks. This means that data in high-demand can be retrieved quickly, but less-used data is still available. Even this lesser-used information may be faster to retrieve, since the read heads should not need to be working to retrieve as much other information at the same time.
For hybrid drives to operate efficiently, they need to "learn" how various resources are used. During this "break-in" period, they record what is used most, and allocate flash memory space to these resources. For this reason, their performance at first will often seem no different than traditional hard disk drives. However, their efficiency should improve with use.

Potential concerns

• Since the Flash memory is being deliberately allocated to high-use data, it may tend to wear out more quickly than a solid-state drive, since there is less storage for the wear leveling system to work with
• Secure deletion of data ("shredding") may be ineffective, since the wear leveling in flash memory may cause overwrite attempts to be redirected to the wrong place. However, attempting to recover deleted data may also be difficult due to wear leveling as well.

Hybrid configurations

Rather than using a hybrid drive, some people use a pair of drives, one solid-state, one hard disk. This dual-drive setup can be used in the same way as a single hybrid drive. Although and user can manually put high-use files on one drive and low-use files on another, there are also ways to configure the operating system to do this automatically. Alternatively, a hardware chip (usually PCIe) can be used to perform this task. In this case, the system will be unaware that multiple drives are being used, much as it would be when using a RAID card.