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by caw
4911 days ago
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EMC uses RAID5 as the default for storage arrays, and then has some number of global hot spares. Netapp uses RAID6 by default, and then also has some number of hot spares. I've never had data loss from either system as a result of multi-drive failure. RAID5 is perfectly fine in most instances. Desktop drives will drop out of RAID arrays frequently, so you have to use RAID6 if you choose to go that route. If a disk drops into deep checking mode for physical errors, then it won't respond to the RAID controller fast enough, and then be considered a dead drive. It will subsequently be re-detected, and then array has to be rebuilt. |
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If you're using low capacity, enterprise class SAS drives, mostly, yes. However when using large capacity SATA drives, it most definitely isn't.
SATA drives (even "enterprise" SATA drives) have an official unrecoverable error rate of 1/10^14. From my experience, the truth is more like 1/10^13.
10^13 bits is roughly 10 terabytes. That means that every time you're reading 10 TB, you are statistically certain to encounter an unrecoverable bit error (and have a 1% chance of having 100 errors, of course). In the case of a rebuilding 10 TB array (only a couple 3 or 4 TB drives) using RAID-5, that means that you're almost sure to have an ECC error that will prevent you from ever rebuilding properly without corruption.