Information Technology Reference
In-Depth Information
At Least Be Open to Change
Even if you exclude a VM or several VMs from participating in the automation of DRS, it is best not
to set VMs to the Disabled option because no recommendations will be provided. A priority 2 recom-
mendation could be provided that suggests moving a VM an administrator thought was best on a
specifi c host to a diff erent host suggested during the migration. For this reason, the Manual option
is better. At least be open to the possibility that a VM might perform better on a diff erent host.
VMware vSphere provides a number of tools to make administrators' lives easier, as long
as you understand the tools and set them up properly. It might also be prudent to monitor the
activities of these tools to see whether a change to the coni guration might be warranted over
time as your environment grows. Monitoring and alarms are discussed in detail in Chapter 13.
DRS is a valuable and useful part of vSphere, and it builds on vMotion to enable vSphere
administrators to be more proactive about managing their environments.
Introducing and Working with Storage DRS
Building on the functionality that VMware introduced in earlier versions—specii cally, build-
ing on Storage I/O Control and Storage vMotion—SDRS introduces the ability to perform auto-
mated balancing of storage utilization. SDRS can perform this automated balancing not only on
the basis of space utilization but also on the basis of I/O load balancing.
Like vSphere DRS, SDRS is built on some closely related concepts and terms:
Just as vSphere DRS uses clusters as a collection of hosts on which to act, SDRS uses data-
store clusters as a collection of datastores on which it acts.
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Just as vSphere DRS can perform both initial placement and manual and ongoing balanc-
ing, SDRS also performs initial placement of VMDKs and ongoing balancing of VMDKs.
The initial placement functionality of SDRS is especially appealing because it helps sim-
plify the VM provisioning process for vSphere administrators.
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Just as vSphere DRS offers afi nity and anti-afi nity rules to inl uence recommendations,
SDRS offers VMDK afi nity and anti-afi nity functionality.
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As just mentioned, SDRS uses the idea of a
datastore
cluster
—a group of datastores treated as
shared storage resources—in order to operate. Before you can enable or coni gure SDRS, you
must create a datastore cluster. However, you can't just arbitrarily combine datastores into a
datastore cluster; there are some guidelines you need to follow.
Specii cally, VMware provides the following guidelines for datastores that are combined into
datastore clusters:
Datastores of different sizes and I/O capacities can be combined in a datastore cluster.
Although possible, we wouldn't recommend this practice unless you have very specii c
requirements. Additionally, datastores from different arrays and vendors can be combined
into a datastore cluster. However, you cannot combine NFS and VMFS datastores in a
datastore cluster.
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You cannot combine replicated and nonreplicated datastores into an SDRS-enabled data-
store cluster.
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