Performance Increase on RAID-5 With Addition of Hard Drives

[CoreyWilson]

Its my understanding that the performance of a RAID5 array will increase as the amount of disks are added to the array - but only to a certain point. Is anyone able to shed a little light as to roughly how many disks can be added to a RAID5 array before the performance starts to degrade?

Also what kind of performance can be noticed by using say a 4 disk raid5 array vs a 7 or 8 disk raid5 array (lets not talk RAID 1+0 in this case as I am aware of the performance differences).

Thanks all

 

[xmsre]

P*N-1 for read performance
P*(N-1)/4 for write performance

Where P is the performance of a single spindle and N is the number of spindles in the RAID 5 array.

For a 10K SCSI drive, use 85. For a 15K SCSI drive, use 130 for P.

Do be aware that as the number of spindles increases, so does the work required by the storage processor/CPU. Different manufacturers have different upper limits and recommended limits for the number of spindles in a RAID 5 array.

 

[comtec17]

Also remember - The wider you go with a RAID Group, the longer the rebuild times.