Information Technology Reference
In-Depth Information
Figure 11.30
Allocating vFlash
Cache to a VM is as
simple as allocating
it as you would CPU
or memory.
As you can see, coni guring and allocating vFlash Cache is a fairly simple task. What won't
be so easy is working out which VM hard disks benei t from allocating vFlash Cache and how
much to allocate. In Chapter 13, “Monitoring VMware vSphere Performance,” we discuss moni-
toring vSphere Performance in great detail. The use of performance graphs and resxtop will be
of great benei t when you start to baseline workloads for vFlash Cache inclusion. Depending on
the workloads that your environment runs, you may i nd that vFlash Cache is of little benei t. In
a low I/O but high memory overcommit, you may i nd that disk I/O is increasing because the
hosts need to swap out memory to disk, just as described earlier in this chapter. In this scenario,
allocating l ash-based resources to swap would be a good idea.
Configuring Swap to Host Cache
Swap to Host Cache, or “Swap to SSD,” is a feature that allocates a portion of local SSD storage to
be the location of a VMs swapi le. As discussed earlier in this chapter, the VM swapi le is very
different from the OS swap/page i le.
One very important point to note—this feature is benei cial only within environments that
have memory contention to the point that the hypervisor has to swap unreserved VM memory
to disk. Based on the i gures explained earlier in this chapter, accessing memory swapped to
disk (even SSD) is still signii cantly slower than accessing it from RAM. That being said, if your
environment i ts within this category, there are signii cant performance benei ts from enabling
this feature.
To con i gure the host for Swap to Cache, a VMFS datastore that has been identii ed as being
backed by an SSD needs to be present. The following steps outline how to enable this feature:
1.
If it is not already running, launch the Web Client and connect to a vCenter Server
instance.
2.
Navigate to the Hosts And Clusters view.
3.
Select the appropriate host.
