SAS 2.0 speed?

Question

Hard disks

There is a shelf for 25 nimble hard drives I plugged the
shelf into the LSI 9260 controller

I consider the speed of the controller:
PCI-ex 2.0 8 lines ~ 4GB
SAS 2.0 4 lines ~ 2.4GB

Run speed in Victoria ~ 750MB and tried to stick all 25 hard drives and only half
This is the same speed only 1 SAS 2.0 line, where does the speed go?

Answer 1

I read that for the maximum speed of raid0 it is necessary that the number of disks be a power of two, check.
If you do not create a raid, is just simultaneous linear reading from all disks at once using dd the maximum?
ps raid0 speeds up only linear reads and writes, but random operations almost do not speed up
what task needs to be solved with 20 disks in raid0 where you need gigabytes per second, a buffer for magnetic cassettes ?, moreover, storing something on such disks is very dangerous , after all, the chances of the entire raid dying due to one disk add up (even the best disks are 0.5%..3% of death), multiply by 20 and get 10%..60%