The timeout = 3 x interval + 1 is a best practice as it allows the server three chances to respond successfully before being marked down. A 5 second interval has been a good place to start as a test request this often shouldn't overload the servers. And 16 seconds is not a horribly long time to wait to mark a failed server down.
If 16 seconds is too long for you to wait to mark a dead member down, you could reduce the timeout or use an iRule to mark the pool member down (LB::down in the LB_FAILED event). If your servers are being overwhelmed with too many requests, you could extend the interval and timeout longer than 5 / 16.
I'd still try troubleshooting why it's failing with the default of 5/16 during a light load test before tinkering too much with the monitor timings.
Aaron
Nimbostratus
