Does a power cut require a parity check?

[SimonAG]

By mistake I turned off the mains power and my unraid lost power and rebooted afterwards and started up without issue. When I started the array it kicked off a parity check, I only just parity checked a few weeks ago as done some new drives and with the weather being hot at the moment, it is not ideal for me to run a parity check. I did cancel the parity check, am I taking a big risk there? There was no writing to data drives going on when the power cut and all the data is fine. 

[kizer]

I always look at it this way personally. 

 

Was I writing any data to the array when I shut down my machine? If not then the Difference between the Data Drives and the Parity should be the same and it shouldn't throw up an error when you run it again. 

 

If your not sure it doesn't hurt to let it go, but often I just cancel and move on. 

[SimonAG]

Does it always throw up a parity check when there is an unclean shut down? Is that just a precaution or is there something that happens on a clean shutdown that makes parity integrity better? 

[kizer]

Yes in MY experience when ever I've encountered an unclean shut down it has always fired off a Parity Check. 

Like I said if I know what the problem was I've often just said cancel and haven't felt any repercussions as long as I know I wasn't performing a write. 

[JonathanM]

44 minutes ago, SimonAG said:

Does it always throw up a parity check when there is an unclean shut down? Is that just a precaution or is there something that happens on a clean shutdown that makes parity integrity better? 

Unclean shutdown means Unraid doesn't know for sure that all writes were completed, so a parity check is automatically started in case there was data in flight when the shutdown occurred.

 

During a clean shutdown, as soon as the array is stopped and all the drives are unmounted, a status file is updated. On array start, that status file is checked and changed to running status.