zfs create: create zvol so slow

[meilihao]

System information

Type	Version/Name
Distribution Name	ubuntu
Distribution Version	16.04.6
Kernel Version	4.4.0-177-generic
Architecture	aarch64
OpenZFS Version	0.8.6

Describe the problem you're observing

zfs create -V so slow. This time it took 4 minutes, and there was 29 minutes before, and no error in syslog.

Describe how to reproduce the problem

unkown

[stale[bot]]

This issue has been automatically marked as "stale" because it has not had any activity for a while. It will be closed in 90 days if no further activity occurs. Thank you for your contributions.