How risky is RAID 5 for my new system?

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phiednate1

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Jun 29, 2013
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So after my old, cramped external harddrive started to fail, I decided it was time to make the leap and setup the home media server I have always wanted. I ended up purchasing a Acer AC100 and 4 x 2tb WD Reds. I figured this would give me about 3tb of room to grow in Raid 5 as I have about 3 tb of media. Since I am new to RAID besides a basic understanding, I have been doing some reading and am now quite confused.

From my understanding, if a drive fails and is replaced, the chance of another drive failing during the rebuild and destroying the raid is quite high. The WD Reds have a failure rate of less then 1 in 10^14 and from a few calculators I found, there is about a 50% chance of a URE and the raid failing when being rebuilt. I realize that RAID 1 is also an option but that leaves me with less space than I wanted.

Is my understanding of all this right and is a 50% chance of failure accurate in the real world? I am willing to accept some risk but it seems like it's a better idea to just go with a JBOD setup and deal with 1 disks data loss in the event of a failure. However, if the real world odds of the raid failing to rebuild are like 10% or ever 20% then this would be fine. Thoughts?
 
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popatim

popatim

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Dec 2, 2009
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You seem to be missing the point. Raid does not replace backups so you loose the raid but not your data because you have it all backed up in multiple locations. The purpose of raid is to keep you going in the event of disk failure not act as a replacement for a backup.

I have never lost a raid and I been doing this a long time. I have no experience with the red drives though so I cant say on their reliability.
 
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phiednate1

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Jun 29, 2013
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I understand that and do have backups (original blurays, dvd and cds). I was planning to utilize RAID as a failsafe against having re-rip CD and Movies in the event of a disk failure. However, if the failure rate of rebuild a RAID 5 is as high as I have found then I am starting to think that rebuilding the data on one drive would be better then using RAID and risk having to redo it all. My suspicion is that the math doesnt reflect real world situations. Also, I noticed a lot of people who say RAID 5 failed them and should be avoided were using WD Green drives or 6+ disks. I am thinking my odds are the raid failing to rebuild is likely less then what I am reading since I am using drives built for the purpose and only 4. Is my thinking off on this?

Really what I am wondering is if RAID 5 is a good idea in my situation.
 
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ss202sl

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May 23, 2012
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I also have never lost a raid due to multiple drive failures (when the servers were monitored). You have to know when a drive fails. I have had a department with a server(they never looked at it) that died one day because the second disk in a raid 5 failed. had they been monitoring the server, the 1st drive would have been replaced before the 2nd one failed.
The failure rate of the drives during rebuilding is not an issue. If it was nobody would be using raid.
 
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