Saved system information while upgrading

origin:
Device:Raspberry Pi
System:Raspbian Jessie
OMV version:3.0.99

now:
I want to upgrade OMV3.X to OMV4.X on Stretch, and I only want my data history saved,like system information about cpu load average,interfaces and disk usage history.
other data is not important.

So,what file should I backup?and migrate it to new OMV4.X？

I found /var/log wrote "/var/lib/rrdcached/db/localhost/**.rrd"
so,I backup /var/lib/rrdcached/db/localhost folder,and move them to the new OMV4.x
That‘s fine.