Database Reference
In-Depth Information
One of our recommendations is to separate your production database from your
development and test environments, if you are able. We also realize this is not always
practical or feasible. Therefore, many times you will have a mixed environment. A
mixed environment is one where you have both your production and nonproduction SQL
server databases on the same physical host.
Figure 7.4
illustrates a mixed environment on a physical host with 64GB of physical
RAM. No matter how many virtual machines are on this physical host, the most physical
memory that will ever be available is 64GB. When you add up the memory demand
footprint of all the VMs, you get 74GB.
Figure 7.4
Mixed workload environment with virtual memory oversubscription.
To help ensure that production workloads are not competing for physical memory from
nonproduction workloads, a memory reservation is set. In
Figure 7.4
, you can see that
40GB has been reserved. As each VM is first started, if it has a memory reservation set
on it, a check is made by the hypervisor to see if a corresponding amount of physical
memory on the host is available so it can be set aside for the exclusive use of that
virtual machine. If the answer is yes, the memory is set aside for the exclusive use of
that virtual machine and is no longer available for use by other virtual machines. If the
answer is no, the virtual machine will not start because the requirement for the memory
reservation cannot be met.
