- Is redundancy key?
- Are you concerned with potential data loss?
- How important is performance?
- How many operations do you expect your system to be performing simultaneously?
- Are they largely going to be read operations, write operations, or both?
Here’s a brief outline of RAID classifications 0 through 5 that will help in your decision making process:
RAID Class 0
RAID classification 0 requires a minimum of two disks. The blocks are striped, so you’ll see excellent performance. There’s no mirroring, therefore there’s no redundancy, so it’s inadvisable to use this for any critical system. Redundancy is a system design in which data is duplicated, so that if it fails, you will have a backup. With RAID Class 0, this means if you lose a disk, you are going to lose all of your data.
RAID Class 1
With RAID class 1, you also have a minimum of two RAID class hard drives. The blocks are mirrored, so you will see redundancy and will not lose all your data if one drive fails. For this reason, it’s widely acceptable to use RAID class 1 for critical systems if you choose.
RAID Class 2
Unfortunately, RAID 2 is not used any more as it’s quite slow and no modern commercial system utilizes it. RAID 2 uses bit level striping called Bit Interleave Data Striping and requires the use of every drive in the array when performing an operation. This inefficiency is one of the main reasons why RAID 2 is no longer used.
RAID Class 3
RAID 3 uses byte level striping wherein sequential bytes are on different drives. This is called Bit Interleaved Data Striping with Parity (also known as small striping). RAID class 3 is slow and cannot handle too many requests for data all at once. Similar to RAID 2, RAID 3 requires the use of every drive in the array when performing an operation. Because of this, RAID 3 is occasionally still used, but this is uncommon.
RAID Class 4
With RAID 4 you see bit level striping, similar to RAID 2, and dedicated parity. RAID 4 typically performs better than RAID 2 and 3 because multiple requests can be processed simultaneously. RAID 4 differs from RAID 2 and RAID 3 because it doesn’t distribute data across all drives when performing a single I/O operation. This allows for faster operations, making it a more appealing option for users.
RAID Class 5
RAID level 5 requires a minimum of three disks. The blocks are striped and there’s good redundancy due to distributed parity. When considering R/W operations, be aware that write operations are going to be slow and read operations will be faster.