well this really depends on what you use mdraid/zfs and as you said alignment. but only for reads.
if you just use dumb mdraid (without too much optimizations configured) (raid 10) + xfs and read/write on top of it you will end up with quite a high memory + cpu usage. but i/o still will be insanly fast.
I've written this more that it works, but its not a put another drive in and done solution. but if you just want to dumb a second drive into it and use mdraid/zfs you will have an overhead. of course if somebody tunes it and builds the application around it you can trim down the overhead significantly.
I've written this more that it works, but its not a put another drive in and done solution. but if you just want to dumb a second drive into it and use mdraid/zfs you will have an overhead. of course if somebody tunes it and builds the application around it you can trim down the overhead significantly.