Many of the IT folk I speak with talk about their storage problems - or, really, their storage problem, because nearly every one brings up the same problem: capacity. They are struggling to keep up with the rate of storage growth.

Hidden inside that problem, though, lies another one: storage performance. Many times, data centers are racing to add storage capacity faster than the growth in actual data would require, spreading data across more disks to maintain acceptable storage performance.

Storage performance is a composite of several things:

* The speed at which the storage system can process requests, or I/O operations per second (IOPS).

* The volume of data it can push through to the requesting entity, or throughput.

* The delay between requesting data and receiving it, or response time.

Processing speed and response time for individual disks are tied to capacity, in that higher-density disks and slower-turning disks typically have higher response times and lower processing rates (fewer IOPS).

For storage systems, as opposed to individual disks, there are ways to engineer around individual disk characteristics to improve different performance metrics.

To improve IOPS, for example, you can stripe data across multiple drives - the RAID-5 approach. Requesting one bit of data each from eight drives simultaneously rather than eight bits sequentially from the same drive gets the complete byte in hand more quickly. Some vendors layer additional cleverness on top of basic striping to improve retrieval rates even more; Xiotech, for example, will allow the striping to spread across as many disks as the storage manager cares to specify, allowing even more parallelization of access.

Striping improves retrieval rates but doesn’t do anything for the minimum response time possible. That is, it can get you the complete block of data requested more quickly, but can’t get the first bits to you any faster - once the storage system receives a request, disks still have to spin, blocks still have to be sought and retrieved using mechanical systems.

To improve that portion of storage latency, a system might use disks that spin faster. A system might manage the amount and location of data on the disks, to optimize seek times, the time spent just moving drive heads without actually reading or writing anything.

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