I see an unexplained opinion that I interpret as "My personal risk analysis together with my wallet says that I can afford to buy more disks and more hardware rather than use a more complex but cost effective solution".
This is part of it but not all, I don't think. I do like the "less complex" part of anything.
Remind me what the I in RAID stands for?
Indigent?
Other people would rather buy 4 1Tb disks to get 3Tb of storage than 6 1Tb disks - your cost/benefit may differ...
Part of my feeling comes from my sense that while many folks should know that RAID != backup, in practice folks get a little lax or forget that they have a RAID config that could fail. In the past 5 years I have seen 7 to 10 postings to mail lists both inside and outside my employment sphere of cries for help to the effect "My RAID 5 is hosed! Does any body have a XXX controller? Does anybody know how to (fill in the blank)?" I think I remember at least 1 Proliant (no idea of actual controller make) and 1 3Ware in these posts. From what I could tell, most of these ended unhappily. A couple were not backed up.
Anyhow, folks used RAID5 with some combination of disks that would be considered small by todays standards (36GB SCSI drives, say) to get a total volume yield that was not attainable in any other way. 300, 500, 750GB or 1TB drives weren't in the picture when some of these were set up, but some of these folks would be completely set for the next decade with 300GB available disk for a given application and they would not need to go to a parity RAID solution to get that.
I also see pretty regular queries fo folks looking to find spare 9, 18 and 36GB SCSI drives to repair or maintain RAID sets that were created man moons ago and that are locked to a particular drive size.
I have an example of backup server that is a 16-drive-slot chassis, but which presently has 8 slots free. By only adding disk as needed (in pairs) we can wait for prices on 1TB drives to sink or wait for 1.5 or 2TB drives. Not locked into the previously affordable drive size.
Anyhow, my arguments are not what I would call scientific. I have a 3TB RAID5 NAS in my care and that is just fine. I don't need same at home. I can't seem to fill up my 500GB mirrored drive set. Using your 3TB example, though, my solution would be to get 2 1TB drives today and then add 2 2TB drives in 2010
I have seen at least one case where somebody set up a RAID5 where I just couldn't fathom why; it was like somebody did it "because I can" or because it was somehow superior. I guess I am on the other end of that opinion continuum.
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