Information Technology Reference
In-Depth Information
including preventing additional VMs from being powered on if there isn't enough RAM
to guarantee 2 GB of RAM to that new VM. However, the RAM greater than 2 GB is not
guaranteed and, if it is not being used, will be reclaimed by the host for use elsewhere.
If plenty of memory is available to the host, the ESXi host will grant what is requested;
otherwise, it will arbitrate the allocation of that memory according to the share values of
the VMs.
Master It
You are coni guring a brand-new large-scale VDI environment but you're
worried that the cluster hosts won't have enough RAM to handle the expected load.
Which advanced memory management technique will ensure that your virtual desktops
have enough RAM without having to use the swapi le?
Solution
Transparent page sharing. TPS ensures that if you have multiple VMs with
the same blocks of memory, you allocate it only once. This can almost be thought of as
“de-duplication for RAM.” Within virtual desktop environments, many VMs are run as
“clones” with their operating system and applications all identical—a perfect case for TPS
to take advantage of.
Manage CPU utilization.
In a VMware vSphere environment, the ESXi hosts control VM
access to physical CPUs. To effectively manage and scale VMware vSphere, administrators
must understand how to allocate CPU resources to VMs, including how to use reserva-
tions, limits, and shares. Reservations provide guarantees to resources, limits provide a
cap on resource usage, and shares help adjust the allocation of resources in a constrained
environment.
Master It
A fellow VMware administrator is a bit concerned about the use of CPU
reservations. She is worried that using CPU reservations will “strand” CPU resources,
preventing those reserved but unused resources from being used by other VMs. Are this
administrator's concerns well founded?
Solution
For CPU reservations, no. While it is true that VMware must have enough un-
reserved CPU capacity to satisfy a CPU reservation when a VM is powered on, reserved
CPU capacity is not “locked” to a VM. If a VM has reserved but unused capacity, that
capacity can and will be used by other VMs on the same host. The other administrator's
concerns could be valid, however, for memory reservations.
Create and manage resource pools.
Managing resource allocation and usage for large
numbers of VMs creates too much administrative overhead. Resource pools provide a mecha-
nism for administrators to apply resource allocation policies to groups of VMs all at the same
time. Resource pools use reservations, limits, and shares to control and modify resource allo-
cation behavior, but only for memory and CPU.
Master It
Your company runs both test/development workloads and production work-
loads on the same hardware. How can you help ensure that test/development work-
loads do not consume too many resources and impact the performance of production
workloads?
Solution
Create a resource pool and place all the test/development VMs in that re-
source pool. Coni gure the resource pool to have a CPU limit and a lower CPU shares
value. This ensures that the test/development will never consume more CPU time than
specii ed in the limit and that, in times of CPU contention, the test/development environ-
ment will have a lower priority on the CPU than production workloads.
