- What is Write Amplification (WAF)?
- How to calculate it.
- What does it mean and represent.
- 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.
The following formula shows how to calculate the WAF of a drive:
Write_Amplification_Factor = NAND_Writes_GB / Host_Writes_GB
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.
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
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