530 NAND Write is 4 times bigger than HOST

Hello, everyone:

I bought an Intel SSD 530 240G for my laptop a month ago. It worked well with the Win8.1 Pro x64， and I use bitlocker.

But,look at this picture.

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Total host writes is 337G,and total NAND writes is 1604G。

1604 / 337 = 4.75

Iamreallyconfused.

I want to know what makes this strange condition happen, and what can I do?

Thank you .