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.
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