When 'stripe_size' is the 'right size' - striped device should appear faster,
but telling you what's the best size is some sort of 'black magic'  :)

Basically - strip size should match boundaries of thin-pool chunk sizes.

i.e. for thin-pool with 128K chunksize -  and 2 disks -
I'd assume best result you should get with 64K stripesize (so 2 disks will
make it 128K stripe)  - but it depends on number of hw aspects.

So you will need to benchmark it.