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large write amplification

Hi list,

Recently I run micro tests on LMDB on DC3700 (200GB), I use bench code https://github.com/hyc/leveldb/tree/benches ,  I tested  fillrandsync mode and collected iostat data, found that write amplification is large 
For fillrandsync case: 

IOPS : 1020 ops/sec

Iostat data shows that w/s on that SSD is 8093, and avgqu-sz is ~ 1, await time is about 0.16 ms,  so the write amplification is ~8, which is large to me, can someone help explain why write amplification is so large? thanks