PACE Yourself to Meet Storage Power and Cooling Needs Page 4


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Putting It All Together

SSD is not the catch-all, cure-all solution by itself. If you need a balance of I/O or performance along with storage capacity, high-performance disk drives in the 146GB and 300GB 15,000RPM class are a good fit with 500GB, 750GB and 1TB class disk drives for storage capacity-centric workloads. For example, in Figure 2, you could in the footprint of three standard IT equipment cabinets configure a 221TB three-tier storage solution comprising 1TB of solid state disk, 28TB of high-performance disk and 192TB of high-capacity storage that consumes about 14 kWh of power with about 384 disk drives and several SSD devices.

The missing piece to Figure 2 is a performance indicator in terms of throughput for bandwidth or sequential applications as well as IOPS for smaller, random workloads. One approach I have seen by some vendors is to simply quote the disk drive manufacturer's IOPS and throughput numbers and then aggregate those for the number of disks being used. The thing to watch out for is that you are assuming that the storage controller can actually utilize and leverage the full disk performance capability, which in many systems is surprising not the case.

If you know the performance rating of your storage systems — in other words, what the controllers can actually deliver for useful work — you can determine your IOPS per watt. Otherwise, you can go to the Storage Performance Council Web site and look up the relative performance of various systems, and based on a given configuration, determine the IOPS per watt or energy footprint.

In a different scenario, instead of using three separate storage systems, in roughly the same footprint you could configure a single monolithic three-bay storage array with 480 disk drives (500GB each) for about 224TB of raw capacity consuming about 24 kWh, which would be for storage-centric applications, or for an I/O-intensive environment, use 480 high performance 15K 4Gbps FC 146GB disk drives for about 70TB raw and about 24 kWh. Granted, these are extreme examples to help illustrate the importance of balancing performance, availability, capacity and energy (PACE) consumption to meet your different application service requirements.

Another variable in all of the previous examples is how you configure the storage system in terms of RAID level for performance, availability and capacity, since the various RAID levels affect energy consumption based on the number of disk drives being used. Ultimately, the right PACE balance will vary, as will other decision and design criteria, among them vendor and technology preferences.

When looking at power, factor in the power requirements for cooling the equipment as well as your UPS and other power conditioning requirements. Also, keep in perspective that software has a power profile regardless of how good a vendor's pitch is; software still requires hardware to run on and that hardware still requires power and cooling. Software can also affect your power and cooling profile by how effectively resources are used, or misused, resulting in extra overhead and hardware to support a given level of service.

Infrastructure resource management (IRM) tools can help identify issues as well as opportunities to maximize your existing IT and data infrastructure resources. Storage management software and tools, whether storage system, appliance or operating system-based, including thin provisioning, compression, compaction or de-duplication — more on these and other techniques at a later time.

There is a growing awareness of environmental and green issues, including reducing CO2 emissions, proper disposal of IT equipment and media, energy conservation and reducing or stretching your energy budget for IT equipment and cooling costs. To close with for now, keep performance, availability, capacity and energy (PACE) in balance to meet your various application service requirements so as not to introduce performance bottlenecks or instability (downtime) in your quest to reduce or maximize your existing IT resources, including power and cooling.

Greg Schulz is founder and senior analyst of the StorageIO group and author of "Resilient Storage Networks" (Elsevier).

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