Is RAID 5 a risk with higher drive capacities?
Posted on October 21st, 2008
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There's a very interesting discussion going on over at ZDNet about RAID5 and hard drive capacities. The premise of the discussion is that unrecoverable read errors are uncommon, but statistically, we're approaching disk sizes where it will start to matter. Here's a quote from the blog entry:
"SATA drives are commonly specified with an unrecoverable read error rate (URE) of 10^14. Which means that once every 100,000,000,000,000 bits, the disk will very politely tell you that, so sorry, but I really, truly can’t read that sector back to you. One hundred trillion bits is about 12 terabytes. Sound like a lot? Not in 2009."
That would mean a bad block when trying to read. It wouldn't be such a problem, except when it happens while you're rebuilding a RAID array after a drive failure. New drive failures are 3% for each of the first three years, after that, the rates rise quickly, according to that author and Google,...
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"SATA drives are commonly specified with an unrecoverable read error rate (URE) of 10^14. Which means that once every 100,000,000,000,000 bits, the disk will very politely tell you that, so sorry, but I really, truly can’t read that sector back to you. One hundred trillion bits is about 12 terabytes. Sound like a lot? Not in 2009."
That would mean a bad block when trying to read. It wouldn't be such a problem, except when it happens while you're rebuilding a RAID array after a drive failure. New drive failures are 3% for each of the first three years, after that, the rates rise quickly, according to that author and Google,...
[Read more →]
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