Case Study $13$: Resource Allocation in WSCs and TCO

Concepts illustrated by this case study

Server and Power Provisioning within a WSC

Time$-$Variance of Workloads

Effects of Variance on TCO

Some of the key challenges to deploying efficient WSCs are provisioning resources properly and utilizing them to their fullest. This problem is complex due to the size of WSCs as well as

the potential variance of the workloads being run. The exercises in this case study show how different uses of resources can affect TCO.

$6\mathrm{.}7$ One of the challenges in provisioning a WSC is determining the proper power load, given the facility size. As described in the chapter, nameplate power is often a peak value that is

rarely encountered.

a$.$ Estimate how the per$-$server TCO changes if the nameplate server power is $200$ watts and the cost is $$3000.$

b$.$ Also consider a higher power, but cheaper option whose power is $300$ watts and costs $$2000.$

c$.$ How does the per$-$server TCO change if the actual average power usage of the servers is only $70\%$ of the nameplate power?

$6\mathrm{.}8.$ One assumption in the TCO model is that the critical load of the facility is fixed, and the amount of servers fits that critical load. In reality, due to the variations of server power based

on load, the critical power used by a facility can vary at any given time. Operators must initially provision the datacentre based on its critical power resources and an estimate of how much

power is used by the data center components.

a$.$ Extend the TCO model to initially provision a WSC based on a server with a nameplate power of $300$ watts, but also calculate the actual monthly critical power used and TCO assuming

the server averages $40\%$ utilization and $225$ watts. How much capacity is left unused?

b$.$ Repeat this exercise with a $500-$watt server that averages $20\%$ utilization and $300$ watts.

$6\mathrm{.}9$ WSCs are often used in an interactive manner with end users, as mentioned in Section $6\mathrm{.}5.$ This interactive usage often leads to time$-$of$-$day fluctuations, with peaks correlating to

specific time periods. For example, for Netflix rentals, there is a peak during the evening periods of $8$ to $10$ p$.$m$.$; the entirety of these time$-$of$-$day effects is significant. Compare the per$-$

server TCO of a data center with a capacity to match the utilization at $4$ a$.$m$.$ compared to $9$ p$.$m$.$

$6\mathrm{.}10[$Discussion$]$ Discuss some options to better utilize the excess servers during the off$-$peak hours or options to save costs. Given the interactive nature of WSCs$,$ what are some of the

challenges to aggressively reducing power usage?

$6\mathrm{.}11[$Discussion$]$ Propose one possible way to improve TCO by focusing on reducing server power. What are the challenges to evaluating your proposal? Estimate the TCO improvements

based on your proposal. What are advantages and drawbacks?