Let's suppose we have 2 hard disks and stripe unit size is 64 kb. While doing random read with size 4KB how Raid 0 affects performance? I mean if we are doing random reads wouldn't operating system block IO layer issue IO one by one? If it does how would it improve read performance while every random read touches single hard drive?
For such a small read it doesn't, but then again there's very few raid options that would make a difference to a single 4KB read.
However, computers will generally perform many thousands of such reads at a time and so you can see how in a 2 disk raid0, some of the reads would hit the first disk, and some would hit the second disk on average.
This means, for those times when the reads are on different disks, they can be looked up in parallel, for a total read speed increase of 2x. The more disks you have, the more the speed increase for a parallel read can occur, as long as the data is laid out across the raid in such a fashion that causes as many parallel reads as possible.