Data Redundancy - Some available Software RAID

Here are some available software RAID that we can use to build our NAS. I will briefly talk about it. My choice of software RAID is ZFS.

Windows' Storage Spaces
Storage Spaces supports creation of 3 types of RAID, striping (RAID 0), mirror (RAID 1), and parity (RAID 5). It has thin provisioning which allows us to declare a storage space larger than our physical storage, and will notify us when we are out of physical storage, then all we need to do is to slot in additional harddisk into our system and add it to the storage pool.

Linux MD
It supports RAID 0, RAID 1, RAID 4, RAID 5 and RAID 6. All Linux distro, i.e., ubuntu, redhat, all supports linux MD. The advantage here over Windows' Storage Spaces is that it has RAID 6, and Linux in general is more stable than Windows.

unRaid
Basically it is implemented as a custom Linux MD driver. It uses a custom RAID similar to RAID 4 (RAID 4 defers from RAID 5 only that all parity is stored in a drive instead of distributed). Generally it gives drobo like features, but the free version only supports up to 3 harddisk.

ZFS
ZFS is a combined file system and logical volume manager that includes features such as data integrity, continuous integrity checking and automatic repair, RAID 0, RAID 1, RAID-Z (RAID 5), RAID-Z2 (RAID 6), RAID-Z3 (allow up to 3 harddisk failure). It is open source so there are many free OS that supports it. It also completely eliminates the RAID write hole, a problem in low end RAID card that cause data corruption.