The developers of the Linux kernel have added support for SSD caching. Previously it was possible to use Solid State Drives (SSDs) as a cache in Linux based operating systems but it was done by applications running outside the kernel space.
Caching, especially by using a combination of a HDD and SSD, improves the performance of a computer. Traditionally computers use a HDD to store data and applications. Nowadays HDDs are usually the bottleneck in computers and are often replaced or accompanied by faster but more expensive SSDs.
To get the best of both worlds, cheap storage and great performance, it's possible to use a cheap and small SSD as a cache by storing frequently accessed data on it. The HDD is used for mass storage and data that is infrequently accessed This way data is first written to the SSD which transfers the data to the HDD when appropriate. Also frequently read data can be stored on the SSD resulting in improved read speeds.
At the moment the feature is classed as expirimental. The new kernel release also supports supports RAID 5 and 6 when using the Btrs file system. By adding RAID capabilities in file-system it's possible to introduce features that were otherwise hard to implement.
