Why Exchange 2019 Demands 128 GB Minimum Server Memory

A Recommendation, Not a Restriction

On September 25, I posted an article on Petri.com about the details Microsoft released at Ignite about Exchange 2019, due for release soon. In the text, I said: “The minimum memory recommendation for Exchange 2019 is 128 GB, up from a wildly unrealistic 8 GB previously.” This statement promptly created a stir and many questions flowed into the Exchange product group to ask if 128 GB was really needed to run the new server.

Well, if you read the statement again, you see that the word “recommendation” is prominent. You will still be able to run Exchange 2019 on servers equipped with less memory, but the strong recommendation is that you should give Exchange enough memory to cache as much data as possible. Caching data results in better all-round server performance with faster mailbox access and searches, but the amount of memory used depends on the load you put on the server.

Different Memory Needs

Clearly, a server handling one hundred mailboxes does not need 128 GB and you only need to equip the server with enough memory to handle the anticipated load. That amount might be 32 GB or 64 GB or 128 GB. It all depends on the load, and Microsoft will continue to provide support to customers who deploy Exchange 2019 on servers equipped with less than 128 GB. However, if you have less than the recommended minimum and you run into performance issues, I think it fair to say that you will not find a sympathetic shoulder to cry on if you call support.

The important idea that the Exchange product team wants to get across to customers is that modern software consumes a lot of memory. Users want high performance, they consume more data than ever before, and servers offer more functionality. All of these aspects must be paid for in CPU, I/O, and memory, so do yourselves a favor and make sure that your brand-new Windows 2019 Server Core box that you prepare for Exchange 2019 comes with enough memory to keep email flowing.

Tools to help people model server configurations for Exchange 2019 are not yet available, but you can expect this gap to be filled in the near future as server vendors begin to measure Exchange 2019 performance on their hardware. Of particular interest is how server vendors will deal with the metacache, the SSD-based fast cache that holds up to 10% of database content (see more information here).

And the Link to Office 365?


Why does a blog about Office 365 care about Exchange 2019? Well, Microsoft runs 175,000 mailbox servers inside Exchange Online, and while those boxes run different software to what on-premises customers do, they follow the guideline of having enough memory to do their work. The Exchange Online servers have been running the metacache for about a year now to allow Microsoft to understand how best to tune its operation before releasing the feature to on-premises customers in Exchange 2019. Habits proven in the cloud are worth noting for on-premises deployment…

3 Replies to “Why Exchange 2019 Demands 128 GB Minimum Server Memory”

  1. With the recommended SSD to spindle ratio of 1:3, does it mean it’s worth to stick with 12x 3.5” and 4x SSD per server? How about having servers that could host 16x or even 24x 3.5” spindles but with only 4x SSDs?

    1. I think I would wait for Microsoft to release the configuration tools. They are coming soon, and they’ll answer questions like this by allowing you to model different scenarios.

  2. We run 250 mailboxes with 2.5 TB of emails out of a CentOS 7 Virtual Machine with 16 Gigs of RAM (running on top of a CentOS 7 KVM Host with RAID6 Array of 15K / 3.5″ hard drives)…

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