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RAID 5 Parity Corruption

D

DVDBob

Member
A rather large computer company is telling me that in a RAID 5 array, if a drive fails, and is not replaced soon, parity corruption can occur.

In my years of experience with RAID systems, it was my understanding that the parity information is written to each drive separately, and is used to rebuild a failed drive. If the parity is determined on every write, how can the abscence of a drive cause corruption?

Is this company feeding me a line of bull? (I beleive they are but need some verification) Does anyone have any links they can provide that might explain a little better.


Thanks in advance.
 
RAID5 arrays spread the data across the drive set in a redundant manner. When one drive fails, the redundancy allows reconstructing the data anyway, but the redundancy is gone - meaning that the correction of soft errors suffers, and if one more drive fails, gone are your data.

Do backups, and have spare drives, maybe even "hot" spares. Real RAID controllers manage the stuff for you.

regards, Peter
 
The longer you run in 'critical' mode, the higher the probability of a problem that would lose data or that could prevent you from successfully rebuilding the array. If the RAID card fails with the array 'critical' the replacement card may not be able to recover the array or could result in bad data since the parity can not be assumed to be coherent (double failure has occured... card + drive).
 
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