How to Reduce the Costs of Performance
Large scale applications often require high performing storage devices to deliver data to the software system and the end-user in a timely manner. Where sub-second response time is mandated we often exceed the capacity of the storage devices to perform. Thus vendors created a technique which attained the required speed. Unfortunately for the customer, the method comes at a very high cost. Let me explain their solution to the problem and a new approach to it that will save you a lot of money.
Computer disk storage speeds and read/write performance have improved a great deal almost every year since 1975. Despite these improvements, spinning disks still pose a bottleneck in the IT process. To meet the demand for sub-second performance the storage vendors recommend a technique which they call “wide striping”—a nebulous term meant to confuse executives and hide the ugly costs associated with it. Here is what it is in plain English.
Wide Striping is where you only use a portion of the disks, perhaps 10% to 30%. The data are spread over multiple disks that are mostly empty. This way the read/write heads have less geography to cover and can retrieve or write information much faster. The technique does achieve the performance objectives necessary for the application. But, stop and think about the costs.
You buy the disks, your vendor’s software license fee is based on the total size of the array, you pay for hardware maintenance on the whole thing, and software maintenance on the total size as well. To make it worse, you now consume much more floor space, you must provide power for the entire array, and air conditioning to cool it down. Thus you pay for 100% of the storage capital and operating expenses and use a small piece of it, only 10% to 30 %. And, because it is an important application, we duplicate the array in the data center and replicate it to a remote site—where we duplicate it again. What a waste of money and we have been doing it for years!
Fortunately new technologies have been developed that can save us a lot of money. Known as Flash and Solid State Disk, SSD, they are similar to technologies with which you are quite familiar. They reside in your digital camera, tablet, and/or cell phone, and act like a USB drive. In fact, one systems engineer I spoke to recently had computed that it would take 900 spinning disks to deliver the performance of an enterprise class flash storage unit. These technologies seem to cost more per volume, but do not forget that you get to use almost all of it compared to the wide striping alternative. You can save a lot of money by reclaiming those wide striped, very fast, low capacity utilization disk arrays. Here’s the plan.
Whatever your next planned storage addition, don’t do it. Instead, use those project or upgrade funds to buy a flash unit. Replace the wide striped arrays with the flash unit and use those arrays for the planned project. They now can be used up to 90%, thus the ROA and ROI of those acquisitions are much improved. The flash unit will do the high-performance application, and, as in cases I am familiar with, will deliver 4 to 5 times the performance of the striped array. Implementing this acquisition strategy will reduce both capital and operating expenses.
Be wary, there are more than a dozen flash and SSD vendors on the market and not all flash arrays are created equal. Test them out and ask for references where they have been in production for a year or more. The technical challenges of these new technologies are quite complex.
For a technical explanation see Hu Yoshida’s blog http://blogs.hds.com/hu/2013/12/top-ten-it-trends-for-2014-trend-8.html#more-9299 and the white paper listed in it: http://www.hds.com/assets/pdf/hitachi-white-paper-accelerated-flash-storage.pdf which explains the challenges and solutions quite well from a technical perspective.