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Different types of RAID and RAID levels, advantages and disadvantages

One of the challenging tasks of every system administrator is to strike a balance between reliability and performance when choosing a dedicated server. Some might say choosing a rite Redundant Array of Independent Disks (RAID) option and level is critical, but what is RAID and why is it so important?

Wikipedia defines RAID as “data storage virtualization technology that combines multiple physical disk drive components into one or more logical units for the purposes of data redundancy, performance improvement, or both. ”  RAID should be considered as part of a business continuity plan and it improves reliability by replicating the data on one or multiple disks. It also improves the performance by enhancing the read write function from/to one or multiple drives. There are two main component in every RAID setup RAID level and RAID control.

Table below shows some of the most common RAID levels.  

Level Minimum # disks Redundancy Disk space utilization Read speed Write Speed Ideal Application
RAID 0 2 None 100% Fast Fast Image & video editing
RAID 1 2 Yes – 1 disk 50% Fast Moderate DB & critical data
RAID 5 3 Yes – 1 disk ~80% Moderate Slow Archiving
RAID 6 4 Yes – 2 disks ~70% Moderate Slow App server
RAID 10 4 Yes – 1 disk 50% Fast Moderate Critical data

In a nutshell RAID controller task is to control the RAID array, to make sure drives are working as the logical unit and computer recognize it as such. There are mainly two types of RAID controller, software and hardware RAID controller. Software RAID relies on computer CPU to control the read / write process, although sever CPU is supper fast these days but still it creates computation overhead and utilises server resources depending on the RAID level. Hardware RAID controller on the other hand is equipped with internal processor like ARM or ASIC to control the array.

Comparison table below shows some the advantages and disadvantages of different RAID types.

RAID Controller Advantage Disadvantage
Software Low cost, easier to reconfigure the array Slow, changing the failed drive is not easy, not suitable for RAID 5 & 6
Hardware card Faster read / write, replacing failed disk is easy Requires additional hardware
Hardware card+ cache Improves I/O performance Cost , susceptible to loss of data in case of power failure