[Linux-cluster] Aggregated or multiple volumes?

[isplist at logicore.net]

While I realize that the most common answer would be 'depends on what you need 
or are doing', I am curious as to how others go about this. 

In my dev setup, I have three FC chassis with 1TB of storage on each. One of 
the chassis act's as the RAID controller for the other two. I can have one 
large volume or many small one's. 

My storage/GFS needs are mostly based on hosting web/php/mysql services. In my 
case, I've split storage up as one large volume for MySQL and two smaller 
one's for web and then mail services. 

It would be simpler to have one single large volume but I'm not sure about 
performance or other things such as security. If someone made it in, they 
would have access to only one area, web or mail or mysql for example.

What are some of the reasons to use either way, multiple or single volume? 

Mike