- RAID 0 – Striped set with no fault tolerance
- RAID 1 – Disk Mirroring
- RAID 1 + 0 – Nested RAID
- RAID 3 – Striped set with parallel access and dedicated parity
- RAID 5 – Striped set with independent disk access and distributed parity
- RAID 6 – Striped set with independent disk access and dual distributed parity
Comparing RAID Levels
RAID 1 offers good performance but comes with a 50 percent RAID capacity overhead. It’s a great choice for small-block random workloads and does not suffer from the write penalty.
RAID 5 is block-level interleaved parity, whereby a single parity block per stripe is rotated among all drives in the RAID set. RAID 5 can tolerate a single drive failure and suffers from the write penalty when performing small-block writes.
RAID 6 is block-level interleaved parity, whereby two discrete parity blocks per stripe are rotated among all drives in the RAID set. RAID 6 can tolerate a two-drive failure and suffers from the write penalty when performing small-block writes.
The detailed description of the above RAID levels and their use cases are explained in the next posts
Less Commonly used RAID Levels
Some RAID levels are not commonly used in today’s data centres either due to complexity or cost issues. The other types of RAID levels which are not or rarely in use are
RAID 2 is bit level striping and it is the only RAID that can recover from single-bit errors.
RAID 3 performs parity at the byte level and uses a dedicated parity drive. RAID 3 stripes data for performance and uses parity for fault tolerance. Parity information is stored on a dedicated parity drive so that the data can be reconstructed if a drive fails in a RAID set
RAID 4 is similar to RAID 5. It performs block-level striping but has a dedicated parity drive. The common issues with using dedicated parity drives is that the parity drive can become a bottleneck for write performance. Every single block update on each row requires updating the parity on the dedicated parity drive which can cause the parity drive to become a bottleneck. One advantage of this type of RAID is that it can be easily expanded by adding more disks to the set by only rebuilding the parity drive.
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