Information Technology Reference
In-Depth Information
Making best use of SSDs
Even though both vFlash Cache and Swap to Host Cache can be confi gured on the same SSD, some
thought should go into how to get the best use of this limited resource.
If your VMs have high memory contention and swap to disk often, your SSD datastores would be
best allocated to Swap to Host Cache. However, if your VMs are I/O constrained and experience
high latency when reading or writing to disk, it would be better to allocate the SSD to vFlash Cache.
In the end, each environment is diff erent. Be sure to think about where your SSDs are allocated
and you will be sure to get the most out of your fastest storage device.
Throughout this chapter, we've shown you how to use reservations, shares, and limits to
modify the resource allocation and resource utilization behaviors of VMware vSphere. In the
next chapter, we'll show you some additional tools for balancing resource utilization across
groups of servers.
h
e Bottom Line
Manage virtual machine memory allocation. In almost every virtualized datacenter,
memory is the resource that typically comes under contention i rst. Most organizations run
out of memory on their VMware ESXi hosts before other resources become constrained.
Fortunately, VMware vSphere offers advanced memory-management technologies as well as
extensive controls for managing the allocation of memory and utilization of memory by VMs.
Master It To guarantee certain levels of performance, your IT director believes that all
VMs must be coni gured with at least 8 GB of RAM. However, you know that many of
your applications rarely use this much memory. What might be an acceptable compro-
mise to help ensure performance?
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?
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?
Create and manage resource pools. Managing resource allocation and usage for large
numbers of VMs creates too much administrative overhead. Resource pools provide a
 
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