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Raid 1 for 4 drives
Hi, This may be a dumb question but I cannot seem to find the answer online.. I have a readynas 104 and I want to set it up so HDD 1 and 2 are in RAID 1 and 3 & 4 are their own RAID 1. the ...
Yes . Raid 1 for one and two HDD , another Raid 1 for 3 and 4 HDD can be done . To do this , Need to Disable XRAID , Delete the Volume created (Make sure you have a backup of your data before doing this) . Select 1 & 2 HDD , Give a Volume name & Create . Select 3 & 4 Create another Raid 1 . (Let one volume sync be completed fully before creating the second since your device has less processor power to handle both) .
I don't understand how you can have full redundancy if you haven't got double the space of where the data is kept?
My only other logic here is simplicity in terms of having two mirrors so it a drive fails I can simply replace it and be up and running again quickly.
My only other logic here is simplicity in terms of having two mirrors so it a drive fails I can simply replace it and be up and running again quickly.
jhsg wrote:
I don't understand how you can have full redundancy if you haven't got double the space of where the data is kept?
That's because you don't understand RAID-5. But the short answer is that you would in fact have redundancy that would allow any drive's content to be rebuilt from the remaining drives.
Here's the key idea: Imagine you have 3 numbers (A, B, and C) that you'd stored. A is on drive 1, B is on drive 2, and C is on drive 3. Now let's store S=A+B+C on drive 4.
If one of the drives is replaced, you can reconstruct the missing number. Depending on the drive you replace, it's one of these equations:
Drive 1: A=S-B-C
Drive 2: B=S-A-C
Drive 3: C=S-A-B
Drive 4: S=A+B+C
There's a bit more to it, but that's the key idea for RAID-5.
In your scenario, the drives are of unequal size. So xraid divides the 4 TB drives into 2 TB pieces.
The two "bottom" 2 TB pieces is used (with the 2 TB drives) to create a 4x2TB RAID-5 array that works like I described above. That is a bottom RAID "layer".
The two "top" 2 TB pieces are used to create a top 2 TB RAID-1 mirror.
The NAS then puts the BTRFS file system on top of both layers, so you only see one volume.
If you upgrade one of the remaining 2 TB drives to 4 TB later on, the NAS will convert the top layer to RAID-5.
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