Well… first off, I’m not sure why they would think multiple Exchange servers is necessarily a bad thing other than a cost of goods issue, but that aside…
Background:
The primary problem with cramming everything onto one box is performance and resource needs. Keep in mind that not only is Exchange on the box along with Unity but you also have voice board drivers, a web server doing the SA/AA/Status monitor stuff, possible TTS processes, possible fax server and fax ports/driver on the box, could be a PDC/BDC as well. All these things take memory and CPU cycles.
The over arching assumption in our product configuration testing is that voice mail is a real time process and that excessive delays or pauses are not an acceptable thing. If your email is delayed a minute or two getting to your client, no big deal. If, on the other hand, you have to wait 60 seconds to get the first voice mail in your inbox, that’s not OK. Looking back over some posts, delays of 10 or 15 seconds stress folks out…
With that in mind, all our load and performance testing in the lab measures timings at several critical sections in the conversation (getting message counts, the time between beep and record, the time to start hearing the first message stream etc…). We set minimum thresholds we consider acceptable and then run tests of various configurations on several different hardware platforms. From this data comes the product configuration document (PDC) which is the bible for what we will support in the field.
Answer:
No, you cannot install Unity on a server that does not have Exchange on it. There are no exceptions to this. We need the local Exchange copy for performance reasons. Early on we tried “pointing” at an Exchange server off our box and it works, of course, but the network connection quickly became a nasty bottleneck and we were not able to handle very many ports/users. Also, if the network connection went down for some reason we couldn’t take calls. Today if the network goes down you can’t check your voice mail from over the phone but we can continue taking calls and messages while the remote servers and/or network connection to them are down. We haven’t supported this configuration since 2.0.
We can support an “all in one” solution where everything is on one Exchange server and everyone is homed on our Exchange box. Given that homing users on our box and allowing Outlook clients to attach for client services entails extra over head, we have stricter limits on the numbers of users/ports allowed in that configuration.
A quick look at the 2.4.0 PCD shows that on a Dell 2300, 500 MHz processor with 256 meg of RAM and a SCSI drive we have tested and approved configurations up to 500 users, 48 ports (that would be a LOT of ports for only 500 users!). Up to 2 sessions of TTS are allowed but if you want fax, it must be run on a separate server, it can’t be on the same box. By comparison a Dell G1 with a 400 MHz processor, 256 meg of RAM and an Ultra ATA IDE drive can handle up to 200 users, 16 ports, two TTS sessions and fax must be off box as well.
If they want more than 500 users and a unified messaging environment, they must have all the users homed off box on a separate Exchange server or servers.
I hope this rambling answer has what you need for this customer… let me know if they need more/other information.
Jeff Lindborg
Unity Product Architect
Active Voice
jlindborg@activevoice.com
http://members.home.net/jlindborg
