I just replaced a parity drive with a larger drive. It did a parity sync. I had never heard of that before. I read in the wiki that you should a parity check after the sync, so i'm doing that now.

 

But what exactly is the difference between a parity sync and a parity check?

 

Creation versus check.

'sync' is an old Raid term that means to "sychronize parity with data", that is, to generate the block-wise parity of all the data disks and write it to the parity disk.  Once this has been completed for all blocks, parity is said to be "synchronized" or "valid".