Q What is the effective SSD speed index?

A A measure of how well an SSD performs under typical consumer workloads. Samsung 850 Pro ≈ 100%.

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Measuring SSD performance is not for the faint-hearted. There are a plethora of speed readings available. A disproportionate emphasis can easily be placed on technical readings which don't translate into improved performance for typical users. The effective speed index is a measure of how well an SSD performs under typical consumer workloads: 50% sequential with an emphasis on lower queue depth performance. The details of the calculation are explained below.

Drive performance is broken into the below six categories:

• SeqR = Sequential read speed (queue depth = 1)
• SeqW = Sequential write speed (queue depth = 1)
• 4kR = Random 4k read speed (queue depth = 1)
• 4kW = Random 4k write speed (queue depth = 1)
• 4k64R = Random 4k read speed (queue depth = 64)
• 4k64W = Random 4k write speed (queue depth = 64)

The real world speed index weighs the above factors in the following proportions:

• SeqR=25%
• SeqW=25%
• 4kR=17%
• 4kW=17%
• 4k64R=8%
• 4k64W=8%

These weights were chosen because the majority of consumer IO (approx 50%) is sequential and the least common type of IO is deep queue depth. Consumer workloads rarely go beyond a queue depth of 4.

For comparison purposes here are the popular AS-SSD total score formula (approximate) weights:

• SeqR=5%
• SeqW=6%
• 4kR=6%
• 4kW=9%
• 4k64R=46%
• 4k64W=28%

There is a heavy bias (74%) on deep queue depth performance, something typical consumers are unlikely to benefit from. The AS-SSD benchmark total score is a far better gauge for server rather than consumer workloads.

 

See a current list of SSDs and their effective speeds (Avg. bench) here.