Database Reference
In-Depth Information
it is to ask management for a new physical server because you underestimated the
requirements.
Memory
When it comes to sizing databases running on virtual machines and physical servers, we
will again start with understanding what the current environment supports and can
tolerate as well as the future stated direction. It should come as no surprise that in the
majority of our engagements, we find customers run out of physical RAM before they
run out of physical CPU resources on their vSphere hosts running database workloads.
The exception to this, we have found, is when customers insert flash into the physical
servers. From a design and architectural perspective, you need to understand if there is
a desire and need to implement flash storage inside the physical server. If this is the
case, work with VMware and the flash storage vendor to understand how the
implementation affects the overall memory sizing of the physical hosts and potentially
the consolidation ratio to ensure maximum benefit for your investment.
Balancing the cost of memory versus the number of virtual machines a physical host can
run is an art. As we have stated several times throughout this topic, when we begin to
virtualize database workloads, consolidation ratios are the least important, and they
should not be the primary goal. Again, a good starting point for this is to leverage
VMware Capacity Planner against your physical database servers to get a high-level
understanding of the RAM requirements for a system.
Earlier in this chapter, we discussed reorganization. If this is a strategy you are looking
to implement for your database virtualization initiative, it is critical to use a tool that
can provide per-database statistics. Not all tools are created equal and will report at
different levels of the server. What we mean by this is that some tools work at the
system level, some work at the SQL instance level, and others work at the individual
database level. Make sure the tool you select for this project can provide the granularity
needed for your initiative.
Virtualization Overhead
In addition to understanding what the current environment will require, it is important to
understand the virtualization overhead of running virtual machines and to account for
this in your sizing and management of the physical ESXi hosts.
Table 5.2
is from the
vSphere 5.5 Resource Management Guide and provides a sample overview of the
memory overhead associated with running a virtual machine. It is important to note that
changing either the number of virtual CPUs or amount of RAM assigned to a virtual
machine changes the amount required by ESXi to run the host.
