Wikipedia
IOPS ( Input/Output Operations Per Second, pronounced eye-ops) is a commonly misused and misunderstood performance measurement used to characterize computer storage devices like hard disk drives (HDD), solid state drives (SSD), and storage area networks (SAN). Frequently mischaracterized as a 'benchmark', IOPS numbers published by storage device manufacturers do not relate to real-world application performance.
To meaningfully describe the performance characteristics of any storage device, it is necessary to specify a minimum of three metrics simultaneously, IOPS, response time, and (application) workload. Absent simultaneous specifications or response-time and workload, IOPS are essentially meaningless. In isolation, IOPS can be considered analogous to "revolutions per minute" of an automobile engine i.e. an engine capable of spinning at 10,000 RPMs with its transmission in neutral does not convey anything of value, however an engine capable of developing specified torque and horsepower at a given number of RPMs fully describes the capabilities of the engine.
In 1999, recognizing the confusion created by industry benchmarketeering abuse of IOPS numbers following the release of IOmeter, the Storage Performance Council developed an industry-standard, peer-reviewed and audited benchmark that has been widely recognized as the only meaningful measurement of storage device IO performance; the SPC-1 benchmark suite. The SPC-1 requires storage vendors to fully characterize their products against a standardized workload closely modeled on 'real-world' applications, reporting both IOPS and response-times and with explicit prohibitions and safeguards against 'cheating' and 'benchmark specials'. As such, an SPC-1 benchmark result provides users with complete information about IOPS, response-times, sustainability of performance over time and data integrity checks. Moreover, SPC-1 audit rules require vendors to submit a complete bill-of-materials including pricing of all components used in the benchmark, to facilitate SPC-1 "Cost-per-IOPS" comparisons among vendor submissions.
Among the single-dimension IOPS tools created explicitly by and for benchmarketers, applications, such as Iometer (originally developed by Intel), as well as IOzone and FIO have frequently been used to grossly exaggerate IOPS. Notable examples include Sun (now Oracle) promoting its F5100 Flash array purportedly capable of delivering "1 million IOPS in 1 RU" (Rack Unit). Subsequently tested on the SPC-1, the same storage device was only capable of delivering 30% of the IOmeter value on the SPC-1.
http://storagemojo.com/2009/10/12/1-million-iops-in-1-ru/ http://www.storageperformance.org/benchmark_results_files/SPC-1C/Oracle/C00010_Sun_F5100/c00010_Oracle_Sun-F5100-Flash_SPC1C_executive-summary.pdf
The specific number of IOPS possible in any system configuration will vary greatly, depending upon the variables the tester enters into the program, including the balance of read and write operations, the mix of sequential and random access patterns, the number of worker threads and queue depth, as well as the data block sizes. There are other factors which can also affect the IOPS results including the system setup, storage drivers, OS background operations, etc. Also, when testing SSDs in particular, there are preconditioning considerations that must be taken into account.