Storage location is an important factor when you want to optimize the performance of your virtual machines. There is always a trade-off between expensive storage that offers high performance and high availability and storage with lower cost and lower performance.

Storage can be divided into different tiers depending on a number of factors:

High tier

Offers high performance and high availability. Might offer built-in snapshots to facilitate backups and Point-in-Time (PiT) restorations. Supports replication, full SP redundancy, and fibre drives. Uses high-cost spindles.

Mid tier

Offers mid-range performance, lower availability, some SP redundancy, and SCSI drives. Might offer snapshots. Uses medium-cost spindles.

Lower tier

Offers low performance, little internal storage redundancy. Uses low end SCSI drives or SATA (low-cost spindles).

Not all applications require the highest performance and most available storage, at least not throughout their entire life cycle.

If you want some of the functionality of the high tier, such as snapshots, but do not want to pay for it, you might be able to achieve some of the high-tier characteristics in software.

When you decide where to place a virtual machine, ask yourself these questions:

How critical is the virtual machine?

What are the virtual machine and the applications' I/O requirements?

What are the virtual machine point-in-time (PiT) restoration and availability requirements?

What are its backup requirements?

What are its replication requirements?

A virtual machine might change tiers during its life cycle because of changes in criticality or changes in technology that push higher-tier features to a lower tier. Criticality is relative and might change for a variety of reasons, including changes in the organization, operational processes, regulatory requirements, disaster planning, and so on.