RAID: Redundant Array of Independent/Inexpensive Drives.
- RAID can be designed to provide increased data reliability or increased I/O performance, though one goal may compromise the other.
- Usually used: RAID0, RAID1, RAID5, RAID10.
- Minimum 2 disks.
- Excellent performance ( as blocks are striped ).
- No redundancy ( no mirror, no parity ).
- Don't use this for any critical system.
- Minimum 2 disks.
- Good performance ( no striping. no parity ).
- Excellent redundancy ( as blocks are mirrored ).
- Minimum 3 disks.
- Good performance ( as blocks are striped ).
- Good redundancy ( distributed parity ).
- Best cost effective option providing both performance and redundancy. Use this for DB that is heavily read oriented. Write operations will be slow.
- Minimum 4 disks.
- This is also called as "stripe of mirrors"
- Excellent redundancy ( as blocks are mirrored )
- Excellent performance ( as blocks are striped )
- If you can afford the dollar, this is the BEST option for any mission critical applications (especially databases).
This ref by Adaptec is a comprehensive intro to RAID.
This ref recommends strongly RAID10 over RAID5.
- It's recommended to use RAID10 for both Vmware / XEN Virtualization and database servers.
- RAID 10 = RAID 0 + RAID 1. It provides optimization for fault tolerance.
- RAID 0 helps to increase performance by striping volume data across multiple disk drives.
- RAID 1 provides disk mirroring which duplicates your data.
- In some cases, RAID 10 offers faster data reads and writes than RAID 5 because it does not need to manage parity.
RAID10 over RAID5
- RAID 5 costs more for write-intensive applications than RAID 1.
- RAID 5 is less outage resilient than RAID 1.
- RAID 5 suffers massive performance degradation during partial outage.
- RAID 5 is less architecturally flexible than RAID 1.
- Correcting RAID 5 performance problems can be very expensive.
|RAID Level||Total array capacity||Fault tolerance||Read speed||Write speed|
500GB x 4 disks
|1000 GB||1 disk||4X||2X|
500GB x 3 disks
|1000 GB||1 disk||2X||Speed of a RAID 5 depends upon the controller implementation|
This article recommends RAID50 as a compromise between RAID10 (Capacity costly) and RAID5 (write slowly).