How exactly does UnRaid save my data

Agilolfinger · September 16, 2021

Hello Together,

I installed OpenMediaVault on a HP Microserver.

Everhings fine. I set up a RAID 5 with 3 disks and all NAS functions are given.

But then I wanted to run a Windows VM in OpemMediaVault. I got it to run but it's very clunky with KVM and Cockpit and all that stuff.

So I thought maybe unRAID is the better option.

But I don't unterstand exactly how the file system works.

With RAID 5 a disk can fail and I have 2/3 of the overall HDD Capacity.

How many disks can fail with unRAID and what will be my Capacity.

And how does the unRAID file system work at all.

Thank you.

CerealExperimentsLain · September 16, 2021

UnRAID stores your files in a plain file system on the main disck. There are also parity disks that are used to reconstruct data if a storage disk fails. You can add more than one parity disc. UnRAID can survive as many storage drive failures as there are parity discs without losing any data. If you have 1 parity disk, and four storage disks, each 16TB in size, you can store 64TB (4x16) and if one storage disk fails the parity disk will keep you going and you can recover. If you lose two storage discs, there will be no saving the data on the two disks. However, as the data is in plain format on the other disks, the remaining two disks that did not fail can still be read. To have 100% loss of data you will need to lose 100% of your disks.

If you add additional parity disks, you can surive additional storage disk failures. Have two parity disks? You can lose 2 storage discs before lost disks become unrecoverable.

Unlike 'RAID' there is no situation where the RAID can 'collapse' and you will lose 100% of your data, every drive remains readable on it's own if it's operational. You can rip your storage disks out of the machine and read them in another computer just using the XFS file system.

UnRAID allows you to mix and match drives as you want, your parity drive must be at least as large as your largest storage disk. So 1x16TB parity and 1x16TB storage disk plus 4x1TB disks? You have 20TB of usable storage. The storage disks just add up without any 'loss'.