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Old 07-03-2013, 15:30   #6
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Join Date: Sep 2010
Posts: 538
I read this paper a while back I just like to read stuff and I don't like to lose data. That paper had me thinking what to do given I have dozens of multi-terabyte drives with critical data on them.

Here's two articles written by people who appear to be unconcerned about failures while rebuilding a RAID5 array.

They has links to other articles and calculations.

Some posted comments about still being concerned.

KD Mann: In addition, the RAID-5 rebuild process itself is hard on all the drives in the array, not just the “failing” drive, and UREs will increase with drive temperature across the entire array — further increasing the chances of a catastrophic failure.

Finally, with 2, 3 and soon 4TB drives, the amount of time requires to complete a RAID-5 rebuild can now stretch into DAYS! Desktop-class disks weren’t built to withstand that kind of abuse even for a few hours…

Given the ratio of URE probability to disk capacity, RAID-5 is dead, there’s no getting around it. Best to just get used to the idea and get on with life….

Disclaimer: Yes, I do work for a RAID manufacturer, and yes, I have (in the past) designed RAID hardware and software.

And about tape drives, the idea is to backup to devices that have different failure modes and lower failure rates. Backing data to devices that have similar failure rates as the original devices is delusional.

And equally important, faster recovery times. Backing up to the "cloud" sounds cool, but if you need to recover those terabytes, it's going to take a while. If you can perform the calculations to predict probabilities of failures of disk arrays, calculating the time to download your backup is easy.
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