Is RAID5 really such a bad idea for home use?

[Vertigo]

Ok so I'm in the process of building a new server to replace my clunky old box and am faced with that age old decision - RAID 1 or 5?

Now everything I'm reading lately is saying RAID5 is a bad idea and should be steered clear of, with the recommendation usually being RAID10 instead. I don't need the performance boost of striping so it'd just be basic RAID 1 mirroring in my case.

Now the logic seems to be that, if a drive fails in a RAID 5 array then, once the drive is replaced, the rebuild process puts a very high load on the remaining drives, which increases the probability of a second drive failing, at which point you're screwed.

Whilst I get that, surely the same applies to a basic mirror too? The entire contents of the surviving drive would still have to be read in order to rebuild the mirror so surely there's just as much chance of failure?

Cost is obviously a big consideration and, given that I need a decent chunk of space, it feels very galling having to halve the effective capacity with a mirror when I could get more bang-for-buck with a parity array.

If there are real, tangible benefits to the mirrored approach then I'd still consider it but I'm struggling to justify it right now.

Any thoughts?

 

[Vertigo]

Well, amongst other stuff, I have a fairly large media library which would be a total pain to lose.

As I'd need as much space again to back it up, I may as well have two drives in a mirror as I then don't need to faff about taking backups. (Critical data is backed up offsite anyway).

I do understand that redundancy and backups are not the same thing but, in my case, the former suits better.

 

[Vertigo]

Well I've done some more snooping and this is how I understand it:

When a RAID 5 array rebuilds following the replacement of a single failed drive, the entire contents of every other drive needs to be read in order to reconstruct the lost parity data. As a result, the higher the number of drives in the array, the higher the chance that an unrecoverable error will be encountered somewhere, potentially causing the rebuild to fail.

With a basic RAID 1 mirror, whilst the entire contents of the remaining drive still need to be read, the simple fact that there's only one drive, as opposed to 2+ in RAID 5, mitigates the odds of a URE being encountered.

RAID 10 offers improved performance due to the striping but I can't see how it provides any better odds of successful rebuild compared to RAID 1.
Unless...
In theory a RAID 10 array could survive a twin drive failure if both drives were on either side of the mirror. In that case then I suppose that if, when rebuilding after a single drive failure, a second drive failed on the other side of the mirror, it could survive that?

Does this make sense?

 

[Vertigo]

Yes I accept that I shouldn't be trusting any critical data to any kind of RAID array.

Anything I literally can't afford to lose is backed up separately and off-site. I'm more concerned with large media libraries which would be a pain to lose but it's not the end of the world if I do. In this specific case, redundant disks work better for me than taking regular backups.