What Is Write Amplification?

Last Updated September 11, 2023

Article

What Is Write Amplification?

How To Calculate Write Amplification

Summary

What is Write Amplification (WAF)?
How to calculate it.
What does it mean and represent?

Resolution

Due to how NAND works, a NAND SSD may need to make more writes than what a user or host asked to write.
WAF is a number to show how much more work the SSD has done than what was asked.
An example is if a user/host writes 4GB to the drive, but the drive had to write 5GB, the WAF = 1.25. An extra GB was written, 25% more than desired.
This overhead eats into the drive endurance.

Formulas

The following formula shows how to calculate the WAF of a drive:

Write_Amplification_Factor = NAND_Writes_GB / Host_Writes_GB

You can use the WAF in these formulas to get more detailed information on an SSD.

Consumed_PE_Cycles = (Host_Writes_GB x Write_Amplification_Factor) / Raw_NAND_Capacity_GB
Host_Write_Endurance_GB = (Raw_NAND_Capacity_GB x Max_PE_Cycles) / Write_Amplification_Factor

NOTE

Write Amplification Factor (WAF) depends on workload and drive configuration.

For 100% sequential write workloads, the WAF is roughly 1.
For workloads that have substantial amounts of random writes, the WAF is higher than 1, because of defragmentation overhead.

Questions?

Contact Solidigm™ Customer Support.