snapraid 12.2

SnapRAID backs up files stored across multiple storage devices, such as disk arrays, in an efficient way reminiscent of its namesake RAID level 4.

Instead of creating a complete copy of the data like classic backups do, it saves space by calculating one or more sets of parity information that's a fraction of the size. Each parity set is stored on an additional device the size of the largest single storage volume, and protects against the loss of any one device, up to a total of six. If more devices fail than there are parity sets, (only) the files they contained are lost, not the entire array. Data corruption by unreliable devices can also be detected and repaired.

SnapRAID is distinct from actual RAID in that it operates on files and creates distinct snapshots only when run. It mainly targets large collections of big files that rarely change, like home media centers. One disadvantage is that all data not in the latest snapshot may be lost if one device fails. An advantage is that accidentally deleted files can be recovered, which is not the case with RAID.

It's also more flexible than true RAID: devices can have different sizes and more can be added without disturbing others. Devices that are not in use can remain fully idle, saving power and producing less noise.