Understanding RAID

RAID – Redundant Array of Inexpensive Disks: Logically puts multiple disks together into a single array. This can increase performance and/or add redundancy.  

Types of RAID:  

Raid 0 Disk striping. No redundancy. Increases performance 

Raid 1 Disk mirroring. Data is duplicated. Good redundancy but requires double number of disks. Good read performance 

Raid 5 Disk striping with parity. High performance and redundancy. At least 3 disks. Lose 1/3 of capacity. Only one disk can fail. If more than that, the logical volume is lost 

Raid 6 Same as 5 but double parity. Protects against failure of more than 2 disks. 

Raid 10 Min of 4 disks. Raid 1+0. Half of usable capacity 

Other Key terms:  

Hot swappable: Replacing failed disks while array is still running  

Hot spare: a spare that is ready to install just isn’t yet. 

Cold spare. A spare that is just the equipment. Not configured yet. Needs to be same size as its replacement.  

Software raid vs hardware raid.  

Hardware raid: controller configures and maintains raid volumes.  

Software raid. No raid controller. OS is controller. Hardware is faster. 

Array controllers. Have dedicated memory. Use battery backed cache. Eliminate single points of failure: have a redundant controller 

Create a server vm with more than one volume.  

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