Information Technology Reference
In-Depth Information
So, what does vSphere need? h e answer is basic—the needs of the vSphere environment are the
aggregate sum of all the use cases across all the VMs, which can cover a broad set of requirements.
If the VMs are
all
small-block workloads and you don't do backups inside guests (which generate
large-block workloads), then it's all about IOPS. If the VMs are
all
large-block workloads, then it's
all about MBps. More often than not, a virtual datacenter has a mix, so the storage design should
be fl exible enough to deliver a broad range of capabilities and capacity—but without overbuilding.
How can you best determine what you will need? With small workloads, too much planning can
result in overbuilding. You can use simple tools, including VMware Capacity Planner, Windows
Perfmon, and top in Linux, to determine the I/O pattern of the applications and OSes that will
be virtualized.
Also, if you have many VMs, consider the aggregate performance requirements, and don't just look
at capacity requirements. After all, 1000 VMs with 10 IOPS each need an aggregate of 10000 IOPS,
which is 50 to 80 fast spindle's worth, regardless of the capacity (in gigabytes or terabytes) needed.
Use large pool designs for generic, light workload VMs.
Conversely, focused, larger VM I/O workloads (such as virtualized SQL Server instances, SharePoint,
Exchange, and other use cases) should be where you spend some time planning and thinking about
layout. h ere are numerous VMware published best practices and a great deal of VMware partner
reference architecture documentation that can help with virtualizing Exchange, SQL Server, Oracle,
and SAP workloads. We have listed a few resources for you:
◆
Exchange
SQL Server
◆
Oracle
◆
SAP
◆
As with performance, the overall availability of the vSphere environment and the VMs
depends on the same shared storage infrastructure, so a robust design is paramount. If the stor-
age is not available, vSphere HA will not be able to recover and the consolidated community of
VMs will be affected.
Note that we said the “consolidated community of VMs.” That statement underscores the
need to put more care and focus on the availability of the coni guration than on the performance
or capacity requirements. In virtual coni gurations, the availability impact of storage issues is
more pronounced, so you must use greater care in an availability design than in the physical
world. It's not just one workload being affected—it's multiple workloads.
At the same time, advanced vSphere options such as Storage vMotion and advanced array
techniques allow you to add, move, or change storage coni gurations nondisruptively, making it
unlikely that you'll create a design where you can't nondisruptively i x performance issues.
