Foreword by Dave Hitz

The ONTAP simulator is great for learning about ONTAP, because you can experiment without jeopardizing a production system or having to justify the budget for a "play system". Instead, just run the simulator on your desktop or laptop, and try whatever crazy experiments you want without risking live systems or live data. Experiment with releases that you aren't ready to put into production. Watch the new release work in your environment. Or play with features or protocols that you haven't licensed on your real systems.

We only recently started letting customers use the simulator, but we've been using it engineering, as a tool to debug and test ONTAP, since the very beginning. Back in 1992, when NetApp started, we designed the very first version of ONTAP to run as a process under UNIX. We wanted to get started writing the software, even though we hadn't yet selected a hardware platform.

We knew that we would eventually be porting to raw hardware, so we designed ONTAP to own the hardware, but we faked out all of the device drivers. We wrote a "disk emulation driver" that opened a file for each "disk" and stored the data there. We used a memory mapped file to simulate non-volatile memory. We put the UNIX network driver into promiscuous mode and used the "network interface tap" (NIT) to grab the raw packets and feed them into ONTAP's own TCP/IP stack. Everything above the device drivers is exactly the same in the simulator as it is in production ONTAP: WAFL, RAID, the TCP/IP stack, CIFS, NFS, iSCSI -- everything. As a result, the simulator faithfully reproduces the behavior of production ONTAP.

Even when we had real hardware for filers, we kept using the simulator because -- for many situations -- it was more convenient. For ten years, the simulator remained an internal debug and testing tool within ngineering, until the folks who run the NetApp University realized that it would be much more pleasant in classrooms if they didn't have the power, heat and noise of a filer for every student. And less expensive too.

Once customers used the simulator in the classroom, they wanted to take it home with them, and that's what inspired us to make it available on the NOW site for all customers.

Have fun!

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Dave Hitz
Co-Founder & VP of Engineering