Hybrid filesystems: BTRFS, ZFS, Drobo

In the realm of file systems, there are currently two main categories: well-known file systems, exemplified by NTFS, EXT, and XFS, and hybrid file systems like BTRFS, ZFS, and, to some extent, Drobo BeyondRAID.

Typical file systems operate solely at the logical level and typically lack awareness of the physical devices they utilize. These file systems occupy allocated space and are unaware of individual disks through a RAID controller. Essentially, they treat all allocated space as uniform.

On the other hand, hybrid file systems (such as BTRFS and ZFS) integrate the functionalities of both a file system and a RAID controller. This integration enables them to optimize hardware capabilities effectively. Hybrid file systems can recognize the distinct characteristics of different physical drives and control their layout down to the level of physical disks. However, this improvement comes with increased complexity in the algorithms for data storage. Notable examples of off-the-shelf devices using BTRFS include NETGEAR ReadyNAS, while NETGEAR ReadyDATA utilizes ZFS.

A third approach involves an array driver that, while not merging with a file system into a monolithic unit, can inspect the file system structure. It adjusts RAID behavior to optimize speed and data integrity. Drobo adopts this approach in its BeyondRAID devices.

Hybrid file systems offer great flexibility, enabling configurations that would be challenging in a typical RAID setup. For instance, one can implement different RAID levels for file system metadata and user files, or even employ distinct RAID levels for individual files. T

However, these file systems come with drawbacks, including their high complexity and the challenge of data recovery in cases of severe metadata damage. Currently, only a limited number of data recovery tools can handle hybrid file systems. If you need to recover data from btrfs, please look at ReclaiMe File Recovery.