Do I have to rebuild parity after starting array with disk missing?

[CaptainTivo]

I made a mistake and have a quick question:

I forgot to stop automatic array start on boot and I accidentally booted with a drive not connected.

Of course, it said "Disk missing" and did not start.  I have since re-connected the drive but I can't remember if, once Unraid has found a drive missing, that it must rebuild parity.  Will it notice that the drive is now connected and assume parity if valid?  Is there any way to tell it to trust the parity?  Or should I just reboot and let it rebuild parity?

Thanks.

[JonathanM]

Since Unraid was running with the missing disk, any writes to that slot updated parity, so the content on the physical disk is no longer in sync with what is emulated. You have 2 options, either throw away any changes to that slot, and rebuild parity from the missing disk, or update the physical disk to match what is emulated by rebuilding the disk. Either choice results in a lengthy rebuild process, your choice whether you want to throw away the data that was written to the emulated copy and revert to an unknown state on the disconnected drive.

 

If the emulated drive is mounted and looks good, it's usually a better choice to rebuild the drive instead of rebuilding parity.

 

All this assumes your drives are all perfectly healthy with solid connections, any failures while in this state will likely cause lost data.

[CaptainTivo]

3 hours ago, JonathanM said:

Since Unraid was running with the missing disk, any writes to that slot updated parity, so the content on the physical disk is no longer in sync with what is emulated. You have 2 options, either throw away any changes to that slot, and rebuild parity from the missing disk, or update the physical disk to match what is emulated by rebuilding the disk. Either choice results in a lengthy rebuild process, your choice whether you want to throw away the data that was written to the emulated copy and revert to an unknown state on the disconnected drive.

 

If the emulated drive is mounted and looks good, it's usually a better choice to rebuild the drive instead of rebuilding parity.

 

All this assumes your drives are all perfectly healthy with solid connections, any failures while in this state will likely cause lost data.

Ok. I was wrong.  I just looked at the screen shot that I made when it happened and the array was actually not started.

It just showed a list of all the drive slots listing the drive numbers that are populated and the one drive that was missing.

So, parity should be good and can just start the array now, right?

Here's a screen shot of main now (after shutdown, re-attaching the disk and booting).

 

[JorgeB]

3 hours ago, CaptainTivo said:

So, parity should be good and can just start the array now, right?

Yes, only if the array was started with a missing disk a rebuild would be required, you can also see that by looking a the disk status, all are green.

[CaptainTivo]

10 hours ago, JorgeB said:

Yes, only if the array was started with a missing disk a rebuild would be required, you can also see that by looking a the disk status, all are green.

Right.  Thanks.