RAID Information

Many people are requesting that RAID be part of a system, but don't thoroughly understand the implications of what they're asking for. The reliability and performance implications of the various RAID levels will be discussed in detail here.

This paper will try to explain the different RAID levels, along with their individual strengths and weaknesses. If goes fairly deeply into the theory and implementation, but diagrams are provided to help.

In this paper, there will be references similar to 'RAID-3' or 'RAID-5'. These are accepted abbreviations for 'RAID Level 3' and 'RAID Level 5', respectively. There are also references similar to 'RAID-2 4+2' or 'RAID-5 6+1+1'. The second part of the reference may be interpreted as '4 data drives and 2 parity drives' and '6 data drives, 1 parity drive and 1 hot standby drive', respectively.

It should be noted that no RAID level, regardless of the redundancy provided, is an adequate replacement for backups. This is because the redundant levels of RAID are designed to solve uptime problems, in that they increase overall system uptime by reducing the number of times that backup media are necessary to restore the system. RAID is not a backup solution, as it can be effected by the most common single cause of data loss, namely user error. Also, RAID is generally difficult to remove from the system, and store in a safe location, such as off-site, or in a fireproof safe.


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