Software Raid Oddity

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I have a CentOS 7.9 system with a software raid 6 root partition. Today something very strange occurred. At 6:45AM the system crashed. I
rebooted and when the system came up I had multiple emails indicating that 3 out of 6 drives had failed on the root partition. Strangely I was able to boot into the system and everything was working correctly despite

> cat /proc/mdstat

also indicating 3 out of 6 drives had failed. Since the system was up and running despite the fact more than 2 drives had failed in the root raid array I decided to reboot the system. Actually I shut it down, waited for the drives to spin down and then restarted. This time when it came back the 3 missing drives were back in the array and a cat
/proc/mdstat indicated all 6 drives were again in the raid 6 array. So a few questions:

1.) If 3 our of 6 drives of a raid 6 array supposedly fail, how does the array still function?
2.) Why would a shutdown/restart sequence supposedly fix the array?
3.) My gut suggests that the raid array was never degraded and that my system (i.e. cat /proc/mdstat) was lying to me. Any Opinions?

Has anybody else ever seen such strange behavior?

2 thoughts on - Software Raid Oddity

  • I wonder if it’s a ram failure in either the main computer or the drive controller. An intermittent ram failure (or cold solder joint or something equally hard to track down) could cause all manner of un-repeatable weirdness.

  • I had an issue similar to this years ago where I helped out a former employer on a Dell Poweredge System with a RAID 5 array (Windows). The system Refused to Boot, but there were lights on the front of the backplane were the drives slid in, indicating drive fault (amber) or drive ok (green).  —
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