2x duplication with 3 drives? Maximum capacity?

[hanime]

I have 3 x 5TB drives added to my pool, and my max capacity says 13.6TB. I have set 2x duplication for the entire pool. Questions:

 

1. How does 2x duplication work with 3 drives? Am I protected if one of the three drives fails?
2. I have 13.6TB in the pool, but I was able to put in 12.9TB worth of files into the pool somehow. It says I have roughly 12.9TB duplicated files and 600GB left. If it's 2x duplication (~25TB), should it have prompted me for more space or something when I reach half of that? Really confused.

[Christopher (Drashna)]

1. 2x Duplication means that the file resides on two disks. 

   If you have three disks, "file 1" may be on disk 1 and 2, "file 2" may be on disk 2 and 3, and "file 3" may be on disk 1 and 3".  

    

   This way, if a single disk fails, you should have a copy of the files on the other disks. 

    

2. It should prompt about this, yes, but I don't think it will, until the disks are completely full.

[hanime]

1. Thank you for clearing that up. It makes more sense now.

By "completely full", does that mean the whole 13.6TB from the pool of three disks I have? How is that possible with 2x duplication, because 2x duplication would take 2x more space, logically. So in my case, I transferred 12.9TB into the pool; with 2x duplication, wouldn't that take up 25.8TB?

[Christopher (Drashna)]

1. Welcome.

    

2. I mean that the pool is completely full. As in no more free space on the pooled disks.

   It will attempt to duplicate the files as best it can with the space available. Once it runs out of space on the disks, and still has files that are not properly duplicated, it will error out and prompt you to add more disks to the pool, IIRC. 

[hanime]

Oops my bad, I was looking at it the wrong way. The 12.9TB includes what is duplicated (as shown in DrivePool interface), which means half of it is what I've copied into the pool. I selected all files and folders within the root of the pool, and check properties to find the file size to be 6.45TB. In essence, 2x duplication will use 2x more space in the pool, 3x uses 3x more, etc.

[Christopher (Drashna)]

Ah okay. Sorry for confusing that.

 

And yeah, in the UI, the "Duplicated" data is the total space used. If you're duplicating everything, the UI will display ... essentially twice the space that you actually are using. (a better way to say this is that it's 2x the unique data on the pool).

 

So if you are using 6.45TBs of actual data, this will definitely show up as 12.9TBs of duplicated data on the pool.