I have a HP DL320 with a MSA60 connected. I would like to increase the read speeds and I was considering moving the journal from the array to the local (much faster) array, and turning on the data=journal option. As I have never done this, I am looking for any advice. My current understanding is that I need to create a device and do something like

mke2fs -O journal_dev /dev/journaldevice
tune2fs -O ^has_journal /dev/sda1
tune2fs -o journal_data -j -J device=/dev/journaldevice /dev/sda1

for the device can I dd a file somewhere? how big (ratio/percent, + the data=journal option)? do I need to add device=/dev/journaldevice to fstab to make sure the move is permanent...if things go bad can I remove the option to revert? what happens to the items in the current journal, I assume I can flush the transactions

Any input, cautions links etc would be great
thanks!

I'm letting you sort out ext4 by sticking with ext3 :-).
The big thing in disk speed is the correct chipset driver compiled in. Post the output of
hdparm -Tt /dev/whatsit