Assign the parity drive to specific user and/or disk

[Deazo]

Hi,

Noob question here, this is my first post.

I have spent the last day discovering and installing UnRaid and things work pretty well and I am very impressed so far.

I have not yet decided to assign a disk to be the parity drive but I will soon do so.

My movies are backed up differently (external HDD) but I would like to continuously protect all other documents.

 

Hence my question:

Can I "assign" this parity drive to "ignore" certain users (e.g. movies) and only protect others (e.g. family pictures) ?

Alternatively I would be happy to assign the parity drive to specific disk(s).

 

I cannot find the option.

 

Thank you in advance.

 

D. 

[trurl]

The parity calculation has no idea about files, folders, etc. It simply treats complete disks as a bunch of bits. Every disk in the array is included in parity, but it is possible to have disks not in the array, either in cache pools, or as unassigned devices. Only cache and disks in the array can participate in the user shares feature, which provides certain benefits, such as having folders which can span disks. Unassigned devices can also be shared on the network, but they don't have the other features of user shares.

 

Have you checked out the introductory material in the LimeTech website? You can get there by clicking on their logo at upper left of any forum page. It has some overview of parity, the array, and user shares.

[Deazo]

Thank you for your answer.

Yes I did take a look at the introductory materials and went through a bunch of information.

 

Just to clarify your answer to me:

If I want to use user share (creating "videos", "pictures", "tax documents", etc.), and if I want these to be spread across drives; these HAVE TO be in the array.

Right?

 

More generally wouldn't you find logical to have the ability to be able to select what type of files you want the parity to treat?

Or is it just me being twisted?

 

Thanks

[trurl]

7 minutes ago, Deazo said:

If I want to use user share (creating "videos", "pictures", "tax documents", etc.), and if I want these to be spread across drives; these HAVE TO be in the array.

I generally think of the array as being only those disks (potentially) protected by parity; i.e., disk1, disk2, disk... So, I don't consider cache to be part of the array. But cache is part of the user shares, and in fact, is one of the features of user shares.

 

9 minutes ago, Deazo said:

More generally wouldn't you find logical to have the ability to be able to select what type of files you want the parity to treat?

Not at all. If you take some more trouble to look into the details of how parity works you would see that what you suggest is impossible. As I said, it just treats all disks as a bunch of bits without regard to the meaning of those bits (folders and files). If it did anything more complicated than that it couldn't be maintained realtime and provide any reasonable performance. And while unRAID isn't RAID, I think you will find that all RAID systems treat their disks as a bunch of bits without regard to the meaning of those bits.

[trurl]

14 minutes ago, Deazo said:

if I want these to be spread across drives; these HAVE TO be in the array.

In order for folders/files on separate disks to appear on the network as if they are all at the same "place" then they have to be in user shares.

[Deazo]

"If it did anything more complicated than that it couldn't be maintained realtime"

 

I understand.

 

My issue is that I am looking at a minimum of 20Tb parity drive, so not (yet) an option for me.

Thanks for the advice, I will keep backing things up manually for now and use unraid mainly as a media server.

 

Cheers

 

[trurl]

5 minutes ago, Deazo said:

My issue is that I am looking at a minimum of 20Tb parity drive, so not (yet) an option for me.

Where did you get this idea? Parity only needs to be at least as large as the largest single disk in the array. Parity doesn't contain any of your data, and parity by itself is incapable of recovering any of your data. The parity calculation requires the bits on the parity disk plus the corresponding bits on all the other disks to calculate the data of a missing disk.

 

I think a lot of users would avoid shooting themselves in the foot if they just took the trouble to understand parity. It isn't very complicated, and many things about how unRAID operates make a lot more sense if you understand parity. Here is a wiki:

 

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

[trurl]

For example, I have 28TB of file storage, but my parity disk is only 6TB.

 

4x6TB + 1x4TB = 28TB data. These are only the data disks in the array, and they can be protected by a single 6TB parity disk. 

[trurl]

13 minutes ago, Deazo said:

I will keep backing things up manually for now and use unraid mainly as a media server.

And unRAID parity is no substitute for backup. Plenty of ways to loose files that don't involve a failed disk, the most common being user error. Sometimes that user error takes the form of people misunderstanding how to use unRAID.

 

You don't have to backup everything, but you should decide what is important enough to backup. This is true even if you have parity.

[Deazo]

Hey Trurl you know what you are right, I think I totally misunderstood how parity works...

I really thought I had to have a drive that is at least the total of all drives.

Just to give you some perspective I only started building my system 2 days ago and I initially started with FreeNAS. It almost broke my brain in half

I then read about UnRAID and it really seduced me.

I did watch the explanations about parity but somewhat today I kept looking at it like a RAID feature.

I will get some sleep and then grasp it all.

Thanks for your patience!

[trurl]

20 minutes ago, Deazo said:

somewhat today I kept looking at it like a RAID feature

The way unRAID calculates parity is very similar to RAID systems. RAID systems don't "backup" your files either. The way parity and data is distributed across disks in RAID (striping) is different than unRAID, but parity in RAID doesn't take up any more space than the size of a single disk. Since unRAID doesn't stripe, it is always possible to read any disk without the other disks, and the disks can be different sizes. But you can't recover a missing disk without the other disks plus parity.

[pwm]

12 hours ago, trurl said:

And while unRAID isn't RAID, I think you will find that all RAID systems treat their disks as a bunch of bits without regard to the meaning of those bits.

The exception would be software like SnapRAID - but SnapRAID isn't performing parity in real time and is instead basically "committing" files to the parity system. So a completely different beast.

 

12 hours ago, Deazo said:

I really thought I had to have a drive that is at least the total of all drives.

The parity is just a "checksum" of the data disks. So one "checksum" can help repair one broken data disk. And dual-parity means the system can recompute the content of two brken data disks.

 

But the parity operates on raw disk blocks. And it will not save you if you overwrite a file or delete a file - the parity will just remember the overwrite or delete so any disk recovery will just recover the disk back to the state with the files overwritten or deleted.

So parity doesn't replace the need for backup. But it gives a chance to repair the disk system after a disk failure. And it gives you better availability since you can continue to access files while the system rebuilds the content of a broken disk onto a new drive.