Nice article, thank you.

I have a question about the write penalty for RAID 1 (mirror). You write: "RAID 1 does have a performance penalty for writes. Each write IOP has to be performed twice (you have to write every piece of data to two disks). " Below, you indicate that the write penalty for RAID 1 is 2.

But I don't understand why a hardware-based RAID controller doesn't simply pipe the same data off to 2 disks simultaneously, reducing the write-time penalty to something much less than 100%? I'd expect there to be some time penalty for the controller to do that, but wouldn't that be significantly less than double the single-disk write time?

Thanks,

Rich