When you buy a data storage, or build your own, say, a RAID, you naturally want it to work fast. I have never met a single person who does like the slow drives.
However, often the real-life read/write speed of a device is somewhat different from the values advertised by a vendor or in case of DIY device from the design-time speed estimation.
There are many reasons why a device performs slower than expected. For example, when analyzing NAS performance, you should take into account the throughput of network to which you connect the NAS. For the external drives connected to a PC via USB, the overall performance will be limited by USB bus which at least five times slower than the slowest hard drive.
However, before you set to find out why your data storage device doesn’t provide the maximum performance, let’s learn how to measure the performance.
The process of measuring various performance characteristics of a data storage device is called benchmarking. The main measured parameters are:
- linear read and write speed – speed at which a device can read or write sequential blocks of data;
- access time – time for which a device spits out the first block of the requested data;
- Input/Output operations Per Second (IOPS) – a number of read or write operations a device handles per second…
Typically, linear read/write speed and access time are represented in charts with maximum and minimum values highlighted; IOPS is usually just a number.
It is very easy to analyze these characteristics – fast device is a device with a maximum linear speed and IOPS, and a minimum access time.