IT managers constantly seek the optimal size of servers that will most efficiently handle their computing workloads. Clearly, if a particular application needs a large memory and can use a lot of processing cores, then a large server seems like the right choice. However, if individual applications do not need such capacity, then a collection of smaller, less costly servers may seem attractive. On the other side of the coin, the cost to power and manage server sprawl has increased dramatically in recent years, making it unacceptable in many cases. The question ultimately comes down to how much to consolidate into each server. IT managers must carefully balance the higher hardware costs and the reduced number of software images to purchase, manage and patch in a large server, against the lower hardware cost, higher software cost, and higher management costs of a number of smaller servers. Does an “economy size” larger server provide the execution efficiency economies of scale to justify the typically higher cost of the higher-end design?
Here at Ideas International, we deal with server pricing, energy efficiency, and performance, so we thought we would provide some basic calculations to illustrate some of the costs involved in determining the optimal size of servers. Note that we are not attempting a comprehensive TCO analysis, which is beyond the scope of a blog. For this exercise, we selected the HP ProLiant DL785 G6 and four DL385 G6 servers. We could have selected IBM servers because they have an industry-standard server that can scale to eight sockets, but we felt that HP was a better example because the DL785 G6 can scale within the same physical box. Next, we loaded each configuration to its maximum number of six-core “Istanbul” Opteron processors, populated a total of 32GB of memory, added an equal number of 300GB SAS drives, selected the redundant power options, and loaded Windows 2008 Server (Enterprise Edition). Essentially, the stack of four DL385 G6 rack servers had an identical configuration to the single DL785 G6. And these servers where not stripped configurations; they were configured to host real application loads.
When we looked at the overall hardware cost of our configurations, the four DL385 G6 servers cost a total of $39,796 before any discounts and allowances, and the DL785 G6 cost $55,819. That 29% price differential was to be expected because designing and building eight sockets into a single server requires more technology and engineering than two socket servers. What did surprise us was how small the difference in cost actually was when selecting real-life configurations rather than the low cost entry configurations showcased on HPs’ website. One point worth noting is that the four DL385 G6 servers require four Windows Enterprise licenses at a cost of $2,710 each versus just one license for the DL785 G6. Those license costs have already been factored into the total costs above.
Finally, as a rough gauge of energy costs, we looked at the cost to power the power supplies rather than the more detailed summation of the power consumption of all of the individual server components. In this exercise we ignored the redundant power supplies and concentrated only on the base power options, assuming they were running at 100%. It is important to note that both ProLiants support the optional HP Insight Power Manager to help monitor and regulate power usage. The DL385 G6 has a choice of three power supplies, 460W, 750W and 1200W, and the DL785 G6 only supports three 1200W power supplies. In our case, we selected the 750W power supply for our DL385 G6 configuration due to the two six-core processors, the amount of memory and the two SAS drives. If we had installed more memory and other options, the 1200W would have been a more appropriate choice. Calculations were based on three years of ownership and a commercial power cost of 15.32 cents per kWh (New Hampshire, USA). Power costs were kept constant for all three years, although that is probably an unrealistic assumption.
HP ProLiant DL385 G6 Power Costs
|
Power Supplies (qty of 4) |
36 month power cost (USD) |
|
460W |
$6,800 |
|
750W * |
11,100 |
|
1200W |
17,800 |
*Used in our configuration of four DL385 G6 servers
HP ProLiant DL785 G6 Power Costs
|
Power Supplies (qty of 3) |
36 month power cost (USD) |
|
1200W ** |
$13,300 |
**Used in our configuration of the DL785 G6
The results above show that there really is not much difference in energy cost between the two stacks. The DL785 G6 power costs at $13,300 are roughly the same as the $11,100 for the four DL385 G6 servers.
We were surprised by the relatively small difference in hardware and energy cost between the DL385 and DL785 alternatives. Once the IT Manager has considered all associated costs, including the management of multiple servers, there may not be much cost difference at all between the two options. What that means is if a large server like the DL785 G6 will handle the application stack more efficiently, then the 29% difference in hardware and software cost may not be significant in our opinion. Other driving factors for selecting the DL785 G6 include its ability to run Windows Datacenter and the fact that there is a single entity to manage versus four servers with the DL385 G6. There is also the issue of virtualization efficiency on a large server versus numerous smaller servers. With a common pool of shared compute “headroom,” the larger, eight-socket server may be able to run at higher overall utilization than the smaller, two socket servers.
As IT managers confront the question of choosing the optimal hardware footprint for x86 workloads, they still have a tough decision to make. This pricing exercise indicates that the hardware and energy costs may not be the deciding factor for selecting a larger x86 server instead of multiple smaller servers. Rather, it will more likely be the “soft” costs related to management that will determine whether eight-socket x86 servers make economic sense. While these costs are notoriously challenging to quantify with a generalized approach, the relatively modest pricing premium of the DL785 G6 sets a low hurdle for achieving tangible returns on its investment.
Recent Comments