So, I've always been with the understanding that a RAID 5 style setup should almost never have more than 3 storage drives to 1 parity drive. This has been beaten into my brain for a while now and I fully understood why since drives... fail.

What I don't understand is that school of thought doesn't seem to hold here with Unraid. I'm not complaining but I'd like to better understand why that is?

In my case I have an Unraid array of 4 WD 10TB drives. All White label. 3 of the 4 are He drives. 1 parity and 3 storage. My thought process is/was that to update further, I need 2 more drives, where 1 would be added to parity, and the other to storage. But I'm seeing where people are going with 1 parity for 10+ storage drives. 

Are we at the point now where that's a reasonable ratio? That's personally a little scary to me and I'm wondering why Unraid doesn't seem to allow for more than 2 parity drives.

Hoping someone here can either tell me why this is safe or that there's another way to add parity drives in the future.

Edited November 16, 20205 yr by justdrooit

31 minutes ago, justdrooit said:

people are going with 1 parity for 10+ storage drives

I don't recommend that though it seems to work for many.

 

But, Unraid IS NOT RAID. Each disk is an independent filesystem that can be read separately from all the other disks. This is how Unraid allows different sized disks in the parity array. Even if you lose more disks than parity allows you to rebuild, you haven't lost everything.

 

Multiple disks actually failing at the same time is pretty rare unless you have some serious power connection mistake. Often it is just a bad connection that gets a disk out-of-sync with parity and requires rebuild.

 

If you are careful with connections, diligent with monitoring disk health (setup Notifications), and don't put multiple new disks with possible infant mortality in your server all at once, dual parity will usually be enough.

 

And more parity is even more disks without any capacity increase. More disks require more expense, more hardware to support them, more power, maybe more license. Each additional disk is an additional point of failure.

 

In any case, whether Unraid or any RAID configuration, you must have backups of anything important and irreplaceable.

Yes, I know Unraid is not raid, but follows certain concepts that Raid5/6 does by having a parity drive in case something were to fail with a storage drive, and the ability to rebuild the lost drive with a replacement using the parity drive. I get it. The fact that the drives are readable on their own was the biggest factor in me going with Unraid. And while it isn't specifically raid, it still competes with raid as a platform/service.

Still I see 20+ potential storage slots in Unraid and only 2 possible ones for parity which gets us back to that crazy ratio and potentially pushing it further. The other problem I have with this is very few people, percentage-wise, are using enterprise-grade equipment for this so I'm a little concerned about reliability. I understand the response to what makes it safe, and I am at least partially in agreement, but in my estimation, many more things can go wrong with consumer level mainboards, drives, etc - some of which are starting this project with some age.

Okay so my shorter term game plan will remain the same for now. I have 2 10TB WD drives to put in and I plan to use one for a second parity drive and the other for more storage. Maybe as I continue expanding over the next year or so I'll get past the 6 storage drives and 2 parity and feel confident enough to go to 7 and 8 storage drives. I really think additional parity drives would be a good thing for Unraid to offer.