Re: Huge Data sets, simple queries

Depesz,

On 1/30/06 9:53 AM, "hubert depesz lubaczewski" <depesz(at)gmail(dot)com> 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