On 04/05/2011 08:31, Brad Campbell wrote:

On 04/05/11 13:30, Drew wrote:

quoted

It seemed logical to me that if two disks had the same data and we
were reading an arbitrary amount of data, why couldn't we split the
read across both disks? That way we get the benefits of pulling from
multiple disks in the read case while accepting the penalty of a write
being as slow as the slowest disk..

I would have thought as you'd be skipping alternate "stripes" on each
disk you minimise the benefit of a readahead buffer and get subjected to
seek and rotational latency on both disks. Overall you're benefit would
be slim to immeasurable. Now on SSD's I could see it providing some
extra oomph as you suffer none of the mechanical latency penalties.

Even on SSD's you'd get some overhead for the skipping - each read 
command has to be tracked by both the host software and the disk firmware.

Such splitting would have to be done on a larger scale to make it 
efficient.  If you request a read for 2 MB, you could take the first MB 
from the first disk and simultaneously the second MB for the second disk.