Yes, it is turned on for my v11. It was a new install and not an upgrade. Should it be turned off?
It adds another layer of validation via CRC checks to confirm the data was written to your media successfully.
If it was my enviroment, I would run it to confirm data is validated and the time added to a backup should be minimal
This feature was in V10 but is enabled by default in V11
Keep in mind if is this is your first full to a new deduplication database
You will need a new baseline-
There is overhead there to write the new baseline chunks as nothing new can be referenced.
Once the baseline is established you should see times simimlar to V10 where only new data is written with pointers.
Hope this helps and I would not disable data validation until you rule out other items.