Pay Per Use

As was mentioned in the last chapter, Pay per use (PPU) is different than Instant Capacity and Temporary Instant Capacity because it is actually an alternative lease program in which your payment to HP varies depending on how busy the system is over the course of each month.

Key Benefits

The key benefit of a PPU lease is that virtually all customers will save money compared to a standard lease. In the PPU Program, there is a base payment and a variable payment each month. The base payment is usually roughly half of the cost of a standard lease. The variable payment is based on average utilization over the course of the previous month.

The key things to consider when investigating PPU are that the maximum monthly payment is 105% of a standard lease and even if you have a number of months where you reach that 105% ceiling, you are guaranteed not to pay more than a standard lease over the life of the lease. One other key consideration is that you would have to run a system at over 70% average utilization to exceed the standard lease payment for any month. So consider this question: How many systems do you have that have an average utilization over 70% for an entire month? This includes nights, weekends, and holidays. Clearly, if you have systems that are consistently that busy, Pay per use wouldn't be a good fit. Industry averages are in the 30% range. For these systems, PPU would represent a significant savings.

Key Tradeoffs

The key tradeoffs of the PPU a program include the fact that it is a lease and that you will need to have budgeting flexibility to handle the variability of monthly lease payments.

The first item is pretty straightforwardif leasing a system is a problem, Temporary Instant Capacity has many of the benefits of PPU but can be used on a system that is a capital purchase.

The variable budgeting issue is another of those nontechnical problems that can, nonetheless, make this solution a nonstarter for some companies.

Another tradeoff is that the PPU program requires outbound communication to be sent from the PPU meter to HP from inside your firewall. The communication between the PPU software running on each partition and the utility meter is secure and is all done behind your firewall. The meter can send the utilization data to HP via e-mail or an SSL connection. Many customers choose the e-mail connection because it can be secured at the firewall to be outbound only. So no hole is required in the firewall to make that work. However, HP typically recommends using the HTTPS connection because it provides more reliable connectivity and can be used for auto patching of the utility meter.

Pay Per Use Sweet Spots

The sweet spot for PPU occurs any time you are leasing a system. Since you are guaranteed not to pay more than a standard lease and you have an opportunity to save in any month the system isn't heavily used, there is really no financial risk to choosing this option.

The more you look at it, the clearer it becomes. If you are going to lease a system anyway, you are almost guaranteed to save money with Pay per use. Since you are guaranteed not to pay more than the standard lease, you really shouldn't lease a system that isn't PPU.

Sweet Spot #1: Cost of PPU Will Not Exceed Cost of a Traditional Lease

Because the program carries a guarantee that you will not pay more than a standard lease over the life of the lease, you can't go wrong with PPU.

Another sweet spot is where you have bursty workloads. If you have workloads that have very high peaks, but those peaks are short in duration, PPU can provide significant savings. This is because the 5-minute data is averaged every day for every CPU. All the CPUs are averaged together to get a daily average for the whole server. Then this data is averaged a third time for the whole month. All this averaging means that short-term peaks in load are smoothed out of the result. This means that you can have a system capable of handling a very high peak load but you will only need to pay for the much lower average.

Sweet Spot #2: PPU Benefits Companies with Bursty Workloads

Because PPU uses several levels of averaging, short-term peaks in workloads are smoothed out.

Choosing between Active CPU and Percent CPU Pay Per Use

There are two things to consider here, the PPU cost of the system and the cost of software for the applications you will run on the system. The PPU version 7 release brought the ability to activate and deactivate CPUs even when using the Percent CPU metric. Any CPUs you turn off will contribute 0% utilization to the average that is calculated for the system. The key difference between Percent CPU and Active CPU is that with Percent CPU you pay for the actual utilization of the active CPUs. With Active CPU, you would pay for 100% of active CPUs, whether they were being used or not. This may make Percent CPU seem like an obvious choice, except that the per-CPU cost for Active CPU is lower than it is for Percent CPUprecisely to make up for the fact that active CPUs are rarely running at 100%.

If you are using a workload manager to maintain a particular utilization level, you can expect that it will keep the same number of CPUs active in either case. Therefore, you should compare the pricing of Active CPU and Percent CPU to see which one provides you the best option. Both will be better than a standard lease, but there may be a slight advantage of one compared to the other.

The other consideration is the cost of the software running on the system. If you are using software that is priced on a per-CPU basis, you will want to work with your software vendor to determine if they will support your purchasing licenses for only the number of CPUs that you plan to activate for the software. An example would be a PPU system or partition with 16 CPUs that would use only 12 active CPUs. It is possible that the software vendor would allow you to purchase a 12-CPU license for the software. You would be obligated to pay for additional licenses should you activate more than the 12 CPUs that you have licensed, but if this doesn't happen until many months later, you have deferred that cost until you needed it. This should work for either Active CPU or Percent CPU since both have the capability to turn off CPUs, but you should verify that the software vendor supports both.