June 06, 2015

vSphere Storage Terminologies - IOPS


Performance is represented in storage products by three statistics: throughput, latency and IOPS.

Throughput is the speed of the data transfer into or out of the storage device. It is a measure of the amount of data that can be pushed through a point in the data path in a given amount of time.
  • Expressed as bytes (kilobytes or megabytes) per second in a storage environment
  • The higher the value, the better
Throughput – a measure of the data transfer rate, or I/O throughput, measured in bytes per second or MegaBytes per second (MBPS).

Latency is a measure of how long it takes for an IO transaction to begin from the requesting application’s viewpoint.
  • Measured in fractions of a second
  • The smaller the latency number, the better
Latency – a measure of the time taken to complete an I/O request, also known as response time. This is frequently measured in milliseconds (one thousandth of a second).

IOPS is a measure of the number of storage transactions processed through a system every second.
  • Input Output Operations per Second
  • “How many Input or Output (IO) operations can be performed by the storage device every second”
  • “How often IOs can occur”
  • A measure of how many IO transactions a disk can complete in a second
  • “How often the storage device can perform a data transfer"
  • “How quickly each drive can process IO requests”
  • Measured in Input/Output Operations per Second (IOPS)
  • Varies depending on the type of IO being done
  • The greater the number of IOPS, the better the performance
IOPS – I/Os per second – a measure of the total I/O operations (reads and writes) issued by an application server.

When comparing IOPS, take into account such things as the size of the transaction, and the type of transaction, i.e. sequential vs. random IO, etc.

To calculate per disk IOPS, use the average latency and average seek time. This can be obtained from the disk manufacturer.

Bandwidth vs. Throughput
Bandwidth is the theoretical maximum amount of data that can travel through a 'channel'. Throughput is how much data actually travels through the 'channel' taking into account various overheads. Your Internet Service Provider (ISP) might provide you with a 1 Gbps Internet connection (Bandwidth), however on a particular session, you might only get 50 Mbps download speed (Throughput).


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