Striping is the process of distributing blocks of data across hard drives. Input data is split up into pieces known as striped units. If you refer to this diagram, striped units Block 0 through Block 8 would be considered a stripe.

With a single hard drive, read and write operations can be executed one at a time. The major advantage of a RAID 0 system is the capacity for parallel processing, which allows read and write operations to be executed on each drive at the same time. For example, the owner of this Striped system could access striped units Block 0, Block 1, and Block 2 at the same time.

Mirroring takes all data written to one drive and writes it in parallel to a second drive. This provides the highest redundancy since there is a 1-for-1 copy of all data written. It also provides very high read performance, as both disks can be read in parallel. Write performance is unaffected as although there are two disks writing in parallel, they’re writing the same data twice. The downside to RAID-1 is the high cost, as one must build out twice the capacity that’s actually required. Traditional RAID-1 is also designed for exactly two drives, and as such is limited in how far it can expand storage.

RAIDZ provides redundancy by using parity, allowing data recovery without the need for full duplication on a second drive. It mathematically creates a new block of data across multiple disks, so if one drive fails, the RAID controller can reconstruct the missing data from the remaining drives. RAIDZ supports single parity, enabling the system to continue functioning even if a drive fails, with parity distributed across the disks to balance access and improve performance. While RAIDZ offers high storage capacity and reliability, performance is slightly reduced due to the calculations required for reading and writing data.

While RAIDZ protects against a single drive failing and can rebuild it, RAIDZ2 uses two different sets of parity calculations and can rebuild an array even with two simultaneous failures (what’s known as N+2 redundancy). RAIDZ2 requires at least 4 drives – at least two for data, and two for the parity information. RAIDZ2 makes the most sense when used with more disks — up to a point. While the efficiency rises with the number of disks, so does the chance of multiple failures and the complexity of rebuilding the disk set. RAIDZ2 has a good balance of capacity, redundancy, and performance, which makes it the workhorse of high-capacity storage.

RAID-Z3 is the most advanced level of RAID-Z, offering triple-disk redundancy. It can withstand the failure of up to three disks without losing any data. RAID-Z3 is ideal for environments where data integrity is critical and cannot afford any data loss.