Depesz, On 1/30/06 9:53 AM, "hubert depesz lubaczewski" <depesz@xxxxxxxxx> wrote: >> double the performance on a reasonable number of drives. > > how many is reasonable? What I mean by that is: given a set of disks N, the read performance of RAID will be equal to the drive read rate A times the number of drives used for reading by the RAID algorithm. In the case of RAID5, that number is (N-1), so the read rate is A x (N-1). In the case of RAID10, that number is N/2, so the read rate is A x (N/2). So, the ratio of read performance RAID5/RAID10 is (N-1)/(N/2) = 2 x (N-1)/N. For numbers of drives, this ratio looks like this: N RAID5/RAID10 3 1.33 6 1.67 8 1.75 14 1.86 So - I think reasonable would be 6-8, which are common disk configurations. - Luke
