Opinions on 4x8Tb RAID 5 please.

[Trexx]

All depends on how good your backup strategy is and how important your data is.

Bigger drives = longer rebuild time. Longer rebuild time = longer risk window of another drive failing.




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[P3R]

24 Tb is a lot of data to backup though.

If backup of the data is a problem, you're trying to store too much of it.

Maybe you don't have to backup all of it? Always do proper multiple backups of the critical data but data can be recreated from other sources may not be necessary to backup.

In the past I successfully rebuilt 4x4Tb RAID 5 twice. It was scary moments.

Then you're depending far too much on RAID.

RAID 5 can only protect from single disk failures. Proper backups will protect from many different threats. Fire, theft, flooding, user mistakes, virus attacks, NAS software bugs, NAS file system corruption and multple disk failures to name some...

Or is it going to fall apart with the first failure.

Of course not but it's much more risk than your 4*4 TB.

[P3R]

So far it looks like with 4x8Tb RAID5 the chance of losing all data is higher than the chance of recovery from HDD failure.

Says who?

I probably wouldn't recommend RAID 5 with that large disks but I'd say that the above statement is a huge exaggeration and FUD.

So I wonder if all 8Tb drive owners switched to RAID 10 or something else.

If they want the best reliability, RAID 6 is better than RAID 10.

[P3R]

Experts?

http://www.enterprisestorageguide.com/r ... uild-times

Oh, so you're in an extremely busy enterprise environment? I didn't think anybody used 4-bay Qnaps for that. The smaller Qnaps are usually only used in home and small business environments, which is a fundamentally different application with different demands, different challenges and different solutions.

In case you're not really in an enterprise environment but more like a home/SMB-situation, a rebuild time of 12 hours or more isn't the end of the world. The NAS is available all the time and usually in home/SMB the systems aren't as heavily used so the slight performance impact won't be an issue either.

http://www.zdnet.com/article/raidfail-d ... ll-arrays/

In 2007 Robin Harris wrote an article called "Why RAID 5 stops working in 2009". In 2009, when RAID 5 was alreday supposed to be dead had he been correct in 2007, he writes the masterpiece you're now showing us mentioning the same issues but not explaining why he was wrong the last time. Several years later he again wrote another article where he said the same thing but added that he used RAID 5 himself!!! Why do anyone believe in that guy anymore?

Robin Harris was/is wrong mainly because of two reasons:
1. His recommendation is for enterprise applications (again not home/SMB usage that's 98 % of the use cases in this forum) but he's referring not to enterprise disks but to the specifications of the very cheapest desktop disks.
2. He gravely misinterprets the specifications when claiming that a disk will have a URE every ~12.5 TB. That's not what the specifications say and more importantly that's not the error rate we see in real life.

Here's someone else that's obviously also fed up with Robin Harris and all the parrots repeating that same BS.

Other people here.

Yes many people aren't technical and experienced enough to see the flaws in all the Robin Harris articles but want to think they're experts anyway and repeat that nonsense over and over. It's done here and in many other places on the net. That however doesn't make it any more correct.

Don't get me wrong, it's a very valid discussion to have if RAID 5 with a specific disk size and number is recommended in a specific application. It's a fact that 4*8 TB is significantly more risky than 4*4 TB but the question is if it's too risky? The answer is that there is no simple answer that fits everyone. It's as wrong to recommend 4*8 TB RAID 5 as it is to say it shouldn't be used at all if we don't look at the other factors that also makes a difference:

• What's the usage? Enterprise environment, home usage, mostly read, mostly write, random or sequential access?
• Whats the importance of the system? Hundreds of users depending on the system professionally or a single user and his toy.
• What's the experience level of the administrator? Enterprise IT-department or a home user that's afraid to touch the NAS and "only want it to work".
• The budget and storage capacity requirements.
• Probably some more things that I can't think of now.

In short, no a 4*8 TB RAID 5 absolutely isn't going to fall apart with the first failure. It may be an okay solution for a non-critical system in a home/SMB application if the administrator is taking care of the NAS correctly and is prepared for the work should a multi disk failure still occur.

[P3R]

By the way... WD announced 10Tb yesterday.

Seagate have had 10 TB NAS disks for a while. I think HGST was first out with 10 TB and they even have a 12 TB now...