Virtualization Storage Design: LUN Sizing

What we often ask in FC storage design is: How big a LUN is, how many virtual machines can a LUN support most?

A common mistake in storage capacity expansion is to focus on meeting capacity requirements and ignoring the impact on performance. I suggest that storage sizing need to consider other aspects of capacity, availability, security, and so on, on the premise of ensuring performance.

A concept and performance index

The image above is a module that is designed for virtual machine access storage in a SAN environment, and there are many factors that can affect the performance of virtual machines. So we are in the design of storage to take into account the various modules, is it possible to have bottlenecks?

Performance Index:

Throughput

The amount of data transmitted over a unit of time. Often measured in Kbps or Mbps.

Latency (response time)

Refers to the time required to complete an IO request. Often measured by milliseconds.

Second storage expansion considerations

SCSI Reservation

It is true that SCSI reservation need special attention before vsphere 4.1 launches Vaai. The VAAI hardware assistedlocking largely avoids the problem of SCSI reservation.

So does this mean that we can use a large LUN, say 64T, and then add the VM indefinitely on that LUN?

Never forget the queues that people tend to overlook.

Queue Queuing

From the image above you can see that there are queues from top to bottom four layers. The longer the queue waits for execution, the longer the response time.

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