Parity Drive Association Question

[Melfox]

I am planning to build an UnRAID server to fill multiple uses: As a Media Server with Plex, an individual file server, and a Time Machine Backup. I want each to appear as a single separate hard drive when I connect to it (ie: 1 media, 1 time machine, and 1 file server), so I plan on using user shares with individual drives assigned to each share (3x4TB for the media server, 1x4TB for time machine, 1x4TB for the file server, and 1x4TB for a parity drive). I am just testing out how this will meet my needs, so the amounts aren't really my concern right now (Plex was the original use until I decided to test multiple things at once).

 

My uncertainty is with the parity drive. If I assign the drives as listed above, does the parity drive cover all of the user shares/the entire array? Can I assign a parity drive to be specifically part of a specific user share or are only the storage drives able to be assigned to a user share (for example, have a parity drive for media, one for time machine, and one for the file server)? I'm thinking long term if I expand out this array with more drives of different sized based on my needs. Seems like it would be simpler to keep each user share as a self contained system. Would that configuration do anything worthwhile for me?

 

I appreciate any assistance that could be provided. As I have yet to build the system or use anything other than Windows and OSX my experience is quite limited.

[pwm]

The parity drive (or parity drives in case you design your system with two) will be responsible for all data disks in the array.

 

You can then decide which of the data disks that should be part of different user shares - the parity drive will not care about how you adjust your shares.

 

If you need to perform any write, that will always affect the parity drive.

But reads can be performed without involving the parity (as long as you don't have a broken drive that needs to be emulated).

 

Having a clear separation of which drives are part of different shares means that while doing just read operations you can perform reads on different shares without them affecting each other (except when you saturate the network card).

[trurl]

Parity covers all disks in the parity array. Parity doesn't know anything at all about user shares, folders, files. Every disk is just a bunch of bits as far as parity is concerned. And parity already allows different sized disks in the array. The only requirement is that parity be at least as large as the single largest data disk.

 

So there is no way to configure parity for separate user shares, and in fact, far from being simpler, it would be much, much more complicated, not only for you, but for the way unRAID actually works.

 

I encourage you to take a little time to try and understand how parity works. It isn't really very complicated, and many things about how unRAID is used and operated make more sense if you understand parity. Here is a wiki:

 

https://lime-technology.com/wiki/UnRAID_6/Overview#Parity-Protected_Array

[Melfox]

Thank you for the information. I am aware generally of how the parity drive works, I just wasn't sure if it would ignore the drives assigned to an specific share. This simplifies my thought process greatly. Much appreciated.