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Last Updated September 11, 2023

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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.

What Is Write Amplification?