[CentOS] mdraid on top of mdraid

> You'll have really poor
> performance if you raid over iscsi...

I've spent more time thinking about this and reading over my
research.The crux here seems to be that while RAID does impose
additional write IOPS costs, it may be more than offset by the read
advantage. According to my own notes (which I overlooked in my first
reply), the increased performance from scaling was part of the
original reason I was thinking of using RAID on top of iSCSI.

Searching more on this, the consensus seems to be that RAID 1/10 on
iSCSI is quite okay and may provide read performance increase but RAID
5's iops penalty will probably be a killer.