Monitoring Disk usage (iowait)
I'm using IOSTAT to check disk load / activity (if there is any).
I have found that the batch-wise processing of calls is very efficient and IO hardly seems an issue.
iostat -x 2 50 to get 50 reports of the iowait (which is the time the Linux kernel get's stuck whenever you have a lot of Synchronous IO in the queue)
In the example you see a very low IO wait and a relatively high CPU load. (%user)
Whenever you find this number is relatively high try to set some write caching on the SAN or use SSD's instead of conventional HDD's