"Sync errors corrected" for parity space bigger than array?

[nearcatch]

Running a correcting parity check and the "sync errors corrected" numbers is increasing a lot, but the parity check is in the space *after* the data. My biggest data drive is 18TB and the parity drives are both 20TB. The check is currently at 18.3 TB. My understanding of parity is that if the parity is bigger than the array, all the *extra* parity should just be 0? No drives are reporting any SMART errors, syslog seems clean other than an odd cron error that has to be unrelated.

deepervisor-diagnostics-20230903-1437.zip

Edited September 3, 2023 by hasown

[itimpi]

There have been previous reports of this space sometimes not being correctly zeroed when the parity is initially built, but I do not think anyone knows why.   I would let it complete this time and not get worried unless it continues to happen in future checks.

[JorgeB]

Did you do a parity swap in the recent past?

[nearcatch]

1 hour ago, JorgeB said:

Did you do a parity swap in the recent past?

Yes, I've done a couple of parity swaps to get the 20TB drives in. My previous parity drives are data drives now.

[JorgeB]

There's known issue where sometimes the new parity capacity after a parity swap does not get correctly zeroed, so the first check will find those errors, it should be fine once you correct them.

[nearcatch]

I precleared the parity drives to stress test them before doing the swaps, so I thought they would've been zeroed anyway. But I'll run a second parity check and see how it goes.

[JorgeB]

14 minutes ago, hasown said:

so I thought they would've been zeroed anyway

It won't matter, bug is that Unraid writes something else instead of zeros to the extra parity capacity during the swap procedure, instead of actually zeroing it.

[nearcatch]

Just following up to finish this thread: the second parity check just finished and 0 errors corrected. Hopefully helps someone in the future who searches for this issue.