Having enough IOPS
IOPS stands for Input/Output Operations Per Second. Essentially, this describes how many operations a device can perform per second before it should be considered saturated. If a device is saturated, further requests must wait until the device has a spare bandwidth. A server overwhelmed with requests can amount to seconds, minutes, or even hours of delayed results.
Depending on application timeout settings and user patience, a device with low IOPS appears as a bottleneck that reduces both system responsiveness and the perception of quality. A database with insufficient IOPS to service queries in a timely manner is unavailable for all intents and purposes. It doesn't matter if PostgreSQL is still available and serving results ...
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