IOPS (Input/Output Operations Per Second) is a common benchmark for hard disks, solid state drives, and other computer storage devices. As with any benchmark, IOPS numbers published by drive and SAN vendors can be manipulated and do not guarantee real-world application performance.^[1]

IOPS can be measured with applications such as Iometer (originally developed by Intel) as well as IOzone and FIO^[2] and is primarily used with servers to find the best storage configuration.

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 random or sequential access patterns, the number of worker threads and queue depth, as well as the data block sizes.^[1] There are other factors related to the system setup, drivers, OS background operations, etc. which can also affect the IOPS results. Also, when testing solid-state drives, there are preconditioning considerations that must be taken into account.^[3]

[edit]Performance characteristics

The most common performance characteristics that are measured or defined are as follows:

For hard disk drives and similar electromechanical storage devices, the random IOPS numbers are primarily dependent upon the storage device's random seek time, whereas the sequential IOPS numbers (especially when using a large block size) typically indicate the maximum sustained bandwidth that a storage device can handle. Often sequential IOPS are reported as a simple MB/s number. Where as:

IOPS * TransferSizeInBytes = BytesPerSec (with the answer typically converted to MegabytesPerSec)

Some hard drives will improve in performance as the number of outstanding IO's (i.e. queue depth) increases. This is usually the result of more advanced controller logic on the drive performing command queuing and reordering commonly called either Tagged Command Queuing (TCQ) or Native Command Queuing (NCQ). Most commodity SATA drives either cannot do this, or their implementation is so poor that no performance benefit can be seen.^{[citation needed]} Enterprise class SATA drives, such as the Western Digital Raptor and Seagate Barracuda NL will improve by nearly 100% with deep queues [1]. High end SCSI drives more commonly found in servers generally show much greater improvement, with the SeagateSavvio exceeding 400 IOPS—more than doubling its performance.^{[citation needed]}

While traditional harddisks have about the same IOPS for read and write, USB Flash drives and most Flash-based solid-state drives are much slower writing than reading due to the fact that FLASH memory must delete the memory block before writing to it.This has caused hardware test sites to start to do IOPS testing, which makes numbers available that have been independently measured.

Newer flash SSD drives such as the Intel X25-E have much higher IOPS than traditional hard disk drives. In a test done by Xssist, using IOmeter, 4KB RANDOM 70/30 RW, queue depth 4, the IOPS delivered by the Intel X25-E 64GB G1 started around 10000 IOPs, and dropped sharply after 8 minutes to 4000 IOPS, and continued to decrease gradually for the next 42 minutes. IOPS vary between 3000 to 4000 from around the 50th minutes onwards for the rest of the 8+ hours test run. ^[4] Even with the drop in random IOPS after the 50th minute, the X25-E still has much higher IOPS compared to traditional hard disk drives.

[edit]Examples

Some ballpark numbers (see e.g. Toms Hardware on Intel X25-M[2] and X25-E[3], and on Fusion-io's ioDrive[4].

[edit]See also

• Instructions per second
• Performance per watt

[edit]References