Exchange Server Sizing Calculator

[emartin40]

Filling out the Exchange Calculator worksheet I get a requirement of 16gb ram, my question is do I need to add more to my ram requirements for the server I'm running exchange on? For example my exchange server is running on windows server 2016 so 16gb is for exchange do I add another 16gb for windows server 2016 for a total of 32gb?

thanks

[#2]

Hi @emartin40. Exchange will be happy use more memory, your user will be happy too with good performance mailbox.  

[#3]

@emartin40 

I would say that 16gb should be more than sufficient.  If you want to take it up to 32gb then go for it, certainly can't do any harm, but 16gb will be fine in my opinion.

[#4 · Accepted solution]

No, the calculator's recommendation covers the OS and Exchange Server. It actually is possible to negatively affect Exchange Server 2016 by giving it more then the optimal/recommended amount of RAM. (Exchange 2019 is a different beast entirely.)

[#5]

@Sam Erde 

Well I must admit I've never heard of that fact before.  That's interesting if so.  Do you have any links to Microsoft documentation that confirms this please?

[#6]

@PeterRising To be fair, this is something that I had read consistently with Exchange 2007 up through 2013. It has been a while since I've sized anything other than 2019, though--so the question of using "too much" memory hasn't been active in my mind for anything other than the new requirement recommendation of 128 GB.

Still, a really quick search turned up these two well-seasoned articles: 

The Exchange Team's blog post "Ask the Perf Guy: How big is too BIG?" touches on the question. it begins with "...we recommend not exceeding the following sizing characteristics for Exchange 2013 servers..." Then, near the end of the post with this statement: "If you do decide to virtualize Exchange, remember to follow our sizing guidance within the Exchange virtual machines. Scale out rather than scale up (the virtual core count and memory size should not exceed the guidelines mentioned above) and try to align as closely as possible to the Preferred Architecture."

Then, the post "Troubleshooting High CPU utilization issues in Exchange 2013" reminded me that the primary oversizing concern actually seems to be around having too many CPU cores. 

The last artifact that I found was an interesting, albeit old explanation about transactional IO vs non-transactional IO: "Why too much memory can hurt Exchange Server 2007 performance", by Brian Posey. TechTarget sits behind a frustrating survey wall, but the crux of his explanation is in the line, "The more physical memory a server has, the longer it takes for the cache to reach its optimal size. Until the cache reaches this point, end users may experience slower-than-normal performance." This, of course, was written in a very different era, so I'd be surprised if the advise is still relevant, given all of the work that has gone into Microsoft's preferred achitecture.

So basically...these provided some interesting re-reading, but I would ultimately focus on the Exchange Sizing Calculator for your specific version of Exchange Server, and simply go with the recommendations that it provides for your specific environment.