Google GKE: Local SSD disk performance is worse than standard persistent disk

We use fio

  fio -ioengine=psync -bs=32k -fdatasync=1 -thread -rw=write -size=10G -filename=test -name="PingCAP max throughput" -iodepth=4 -runtime=60 -numjobs=1 -group_reporting

and find that local disk has a bad performance than persistent disk.

A detailed report https://docs.google.com/document/d/1OP1VnGlQx__jW2i8sLfmZWqf...

Btw, if we remove -fdatasync=1 and use -direct=1 to bypass page cache, the local SSD disk has a better performance.

Interesting. Does anyone know about it?