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Forum Discussion
Failures of various RAID modes.
I'm intrigued by the failures. dbott67 wrote: ........ and 2 multiple disk failures where I had to replace the drives and restore from backup. In each case, I was able to recover without dat...
He just gives his recommendations w/o much underlying analysis. So its a bit hard to know what to do with it (other than decide to follow it blindly or not).
Also, when he compares RAID-6 to RAID-10 safety he is talking about very large arrays ("above roughly 40 TB when consumer drives are used"). That is, with 4 TB drives he is talking 12 drives or more with RAID-6. He specifically sets a 25-disk threshold (for using a storage consultant) further down. Lots of things change when you reach that scale. I'd agree that it is a risky to create a RAID-5 or RAID-6 array with that many disks. Resyncing a 12x4TB RAID-6 volume for instance requires reading/writing 48 TB. RAID-10 would require 20x4TB (a lot more drives), but when you replace a single drive the resync only requires reading/writing 8 TB (copying the associated 4 TB mirror drive).
When he talks about specifically about small business applications at the end (probably similar to most home scenarios) he is clear that RAID-6 is fine for smaller arrays. I've had good luck with RAID-5, and it offers better capacity and performance than RAID-6, though obviously it is not as available. I don't say "safe" because RAID will fail sometimes, and I don't view RAID-5 (or RAID-10) as "safe". RAID is convenient for volume aggregation, and usually keeps data available during disk replacements and expansion. But not safe enough to rely on 100%.
My overall impression from posts in this forum is that NAS failures (power glitches or hard failures) create data loss at least as often as disk drive failures. My own experience reflects this (one of each), perhaps other people can chime in with their history.
Also, when he compares RAID-6 to RAID-10 safety he is talking about very large arrays ("above roughly 40 TB when consumer drives are used"). That is, with 4 TB drives he is talking 12 drives or more with RAID-6. He specifically sets a 25-disk threshold (for using a storage consultant) further down. Lots of things change when you reach that scale. I'd agree that it is a risky to create a RAID-5 or RAID-6 array with that many disks. Resyncing a 12x4TB RAID-6 volume for instance requires reading/writing 48 TB. RAID-10 would require 20x4TB (a lot more drives), but when you replace a single drive the resync only requires reading/writing 8 TB (copying the associated 4 TB mirror drive).
When he talks about specifically about small business applications at the end (probably similar to most home scenarios) he is clear that RAID-6 is fine for smaller arrays. I've had good luck with RAID-5, and it offers better capacity and performance than RAID-6, though obviously it is not as available. I don't say "safe" because RAID will fail sometimes, and I don't view RAID-5 (or RAID-10) as "safe". RAID is convenient for volume aggregation, and usually keeps data available during disk replacements and expansion. But not safe enough to rely on 100%.
My overall impression from posts in this forum is that NAS failures (power glitches or hard failures) create data loss at least as often as disk drive failures. My own experience reflects this (one of each), perhaps other people can chime in with their history.
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