Is there a potential risk of a write hole if there is a loss of power during writing data?

 

It is my understand a power loss/failure could potentially cause a parity problem (not a data problem if using journal or copy on write filesystem; the data just won't be there, so at least you'll know where to start over).

 

Is there any mitigation done with Unraid?

 

Every filesystem potentially has that issue, because after the data to get written is transferred to the drive, the filesystem doesn't particularly care anymore about it, and is relying upon the drive itself to write the data.  

 

Use a UPS on any computer system you care about.  That is the primary defense against this issue, not choice of OS or filesystem