I'm currently upgrading/rebuilding 1 disk. Using dual parity.

 

I'm noticing that unRAID reads both parity disks during the rebuiling process. Wondered why that was necessary? In order to just rebuild the disk, reading 1 parity disk should suffice, no?

 

But following that thought: If we have dual parity and are rebuilding just 1 disk, why not use the opportunity to run a parity check at the same time? So basically use parity 1 to rebuild the disk, and use parity 2 to double check that everything's perfect. That would be 2 jobs done at the same time, with the same speed and the same disk wear.

 

Thoughts?

Edited January 14, 20215 yr by madshi

27 minutes ago, madshi said:

why not use the opportunity to run a parity check at the same time?

That's is what is already being done, hence why parity2 is being read.

Oh, that's very cool, thanks for letting me know!

 

Why is there no "error" counter in the statistics, though? Normally, when doing a parity check there's an error counter, and it's nice to see it stay at 0.

 

Will there be an error or success report at the end of this simultaneous "disk rebuild + parity check" action that I have currently running? Can I assume that if unRAID reports no error, the state of the array can safely be considered "perfect", so I don't need to follow up the rebuild with another parity check?

Edited January 14, 20215 yr by madshi

There is no error counter but it will report any errors after it's done, be it rebuild errors or sync errors (or both together).

That's fantastic, thank you!

 

So I would like to reduce my feature request to a very little change: Just add the "error" information to the dual parity rebuild statistics, so that the combined dual parity "rebuild+parity check" procedure looks the same as a normal parity check. This way everybody can intuitively understand that in addition to the disk rebuild, also a parity check is performed at the same time. Which is a *great* hidden feature of unRAID, IMHO, and a nice extra benefit of using dual parity.

31 minutes ago, madshi said:

Can I assume that if unRAID reports no error, the state of the array can safely be considered "perfect", so I don't need to follow up the rebuild with another parity check

What will not have been checked is that the disk being rebuilt can be read back without error.   All you will know is that no write errors were encountered.   You therefore might still want to carry out a (non-correcting) parity check as a confidence test.

Ah yes, that does make sense, thanks.