Ruriko on "[Plugin: W3 Total Cache] Slow disk I/O"

I am running a vps that hosts over 50 sites and all run wordpress with w3 plugin and is set to use APC. I notice it's doing tons of disk queries and it's mostly due to APC. Is there any suggestions to optimize this? cause it's making it have slow I/O

http://wordpress.org/plugins/w3-total-cache/