Redundant Array of Inexpensive Disks Or Redundant Array of Independent Disks
The utilisation of multiple hard drives as to provide data redundancy and improvements in performance.
Combines multiple physical disk components into one or more logical units for the purpose of data redundancy, performance improvement or both.
RAID exists as many different levels. Each one providing benefits dependent on hardware setup, e.g.
- RAID 0
- RAID 1
- RAID 5
- RAID 10
HARDWARE OR SOFTWARE?
RAID can be implemented as hardware or as software.
Both setups still require multiple hard drives
Hardware RAID requires a built in RAID controller card, whereas software RAID requires an operating system or utility that provides the RAID functionality
- Often referred to as striping
- Uses two drives in conjunction with one other for speed
- Data is divided when it is written to both drives so that the workload is balanced, leading to it being more efficient
- There is no redundancy in this method
- Two identical drives should be used - Two different drives can be used, but at a cost.
- For example: If you have an 80GB and a 120GB drive, RAID 0 will have the machine treat them as two 80GB drives, ignoring the extra 40GB of space.
- A minimum of two drives are needed
RAID 0 is ideal for non-critical storage of data that have to be read/written to at high speed, such as on an image retouching or video editing station
- Great performance, both in read and write operations
- Easy to implement
- If one of the drives fails, all data in the RAID 0 array are lost.
- Often referred to as mirroring
- Essentially a failsafe set up for a hard drive
- Two drives are set up so in effect all data is written twice
- If one drive fails, all data is preserved on drive two and the system will remain up and running
- Minimum of two drives are needed
- Two 100GB drives will mean you have 100GB of storage only
- Ideal for mission citical storage, example: Accounting systems
- Excellent read speed and a write-speed that is comarable to that of a single drive
- If a drive fails, data does not have to be rebuilt, they just have to be copied to the replacment drive
- RAID 1 is very simple
- Effective storage capacity is only half the total drive
- Does not always allow for hot swap
- This combines RAID 0 & RAID 1, however it does not use mirroring.
- A parity block across all drives is employed
- If a drive fails the parity, information along with the remaining drive information can be used to rebuild the set
- A minimum of 3 drives is required for RAID 5
RAID 5 combines efficient storage with excellent security and decent performance
Ideal for fiel and application servers that have a limited number of data drives
- Read data transactions are very fast while write data transactions are somewhat slower
- If a drive fails, you still have access to all data, eben while the failed drive is being replaces and the storage controller rebuilds the data on the new drive
- Drive failures have an effect on throughput, although this is still acceptable
- Combines the advantages (and disadvantages) of RAID 0 and RAID 1 into a single system.
- It prvides security by mirroring all data on secondary drives, while using stripping across each set of drives to speed up data transfers
- Requires a minimum of 4 drives
- If something goes wrong with one disk, in a RAID 10 configuration, the rebuild time is very fast as all that is needed is to copy all data from the surviving mirror to the new drive
- This can take as little as 30 minutes for 1TB of data
- Half of the storage capacity goes to mirroring, so it's an expensive way to have redundancy