Performance degradation of ZFS?

[Yasuhiro KIMURA]

Hello,

Last month I upgraded my home server from 11.2-RELEASE to
12.0-RELEASE. It is ZFS only system. After making full data backup
with tar(1) I made clean install of 12.0-RELEASE and restored backuped
data. Then there is significant improvement of I/O performance.

Is it possible that I/O performance degrade while using ZFS for a long
time? And if answer is yes is there any way to recover performance
without making full backup and restore?

Best Regards.

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Yasuhiro KIMURA