conflicting recommendations for read-ahead settings on software raid

From http://www.mongodb.org/display/DOCS/Amazon+EC2+Quickstart

$ sudo blockdev --setra 128 /dev/md0
$ sudo blockdev --setra 128 /dev/sdh1
$ sudo blockdev --setra 128 /dev/sdh2
$ sudo blockdev --setra 128 /dev/sdh3
$ sudo blockdev --setra 128 /dev/sdh4

From http://www.mongodb.org/display/DOCS/Readahead

RAID on EC2: If you are following our Amazon EC2 guidelines, and running with multiple EBS volumes in a software RAID configuration, then the recommendation is to set the readahead to 0 on the volumes that make up the RAID array while setting the readahead to the value you want on the RAID volume itself.