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RAID 5 vs 6 - and unrecoverable read errors

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December 27, 2009 4:45:57 PM

I am getting ready to build a file server after new years and researching different raids. This server is going to be dedicated to Video and Audio and will not be data i want to lose by any means... i could fill 5 TB no problem and was looking at getting SIX 1.5 TB drives. I'm trying to figure out whether to do the raid 5 for more space or RAID 6 for more redundancy... after hours of researching i start reading about unrecoverable read errors during rebuilds and wondering if this is something i should worry about...
a c 415 G Storage
December 27, 2009 7:05:38 PM

The very first thing you need to understand is that RAID by itself is no guarantee of protection for your data. There are all kinds of risks to your data that RAID can't protect against - and that assumes that it works properly. I've seen plenty of posts by people with RAID 5 sets who have lost their data because a drive failed and something screwed up while they were attempting to replace it.

So if the data is really important to you, that means you need to have a second copy of it, preferably offsite. Given that, you might want to spend a little less money on the RAID setup and use the savings for external drives for your backups.
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a b G Storage
December 28, 2009 4:58:36 AM

I second that. A cheap raid 5 maximizes the amount of space you get and gives your some protection against a drive failure. Then spend what you have left over on external storage to store your most important stuff. Just one of the hardware raid cards buys you two 2 TB drives that you can have as a real offline backup.
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a b G Storage
December 28, 2009 7:31:37 PM

There's some articles in Adaptec blog (no longer active) that talks about calculating the chance of unrecoverable error. For a the platter density of a modern 1TB drive, no more than 8 drives should be used in a RAID5 array if I remember correctly.

In either case, RAID redundancy only protects you from drive failure (when it works properly) and does not protect data from other factors as both sminlal and goobaah have both stated. Some form of backup is needed for the data most essential to you.

For example, I currently run a 7x1TB RAID5 array and use a another two external 1TB for backing up more important data. There's something called consistency check and patrol reading on my PERC 5/i (LSI clone) which helps somewhat in preventing those unrecoverable errors I guess.
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January 9, 2010 9:57:27 AM

I realize that a RAID is no substitute for a true backup... I plan on doing DVD backups for most everything...

i was more interested as to opinions on RAID 5 vs 6...

pretty much decided on the RAID 6 now... most likely with eight 1.5 TB drives unless the price comes down on the 2Tb

unless someone has a better idea...?

thnx
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a c 415 G Storage
January 9, 2010 5:15:00 PM

You're willing to buy 12TB worth of storage but plan to do backups on DVDs? Geez, that's a very strange sense of priorities, IMHO...

You realize that, say, 10TB of storage = 2000 DVDs, right?
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January 13, 2010 1:58:56 AM

some dvd some blu ray... data being backed up is movies and music...

the whole point of the RAID 6 though is in hopes that i will never have to worry about restoring the backups...

going to be running linux so hopefully i wont have to deal with malicious acts of others
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