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FAQ: Questions on Pool's HDD usage


So I have several drives in the drivepool with X2 duplication.


I added a new drive about a week ago, and it still shows empty.


I attached a pic of the drivepool.


I also attached a pic of the Balancer settings. Wasn't sure if this mattered or not.


Any ideas on why that newer drive is not being utilized?





Edited by Christopher (Drashna)
Pinning as FAQ, because it is

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With default settings, DP allocates to HDDs with most free space and it seems as if you have added a 1TB drive in a po with rather larger ones that are not filled halfway. It will be quite some time/data before that drive is used.


This is precisely correct.


Specifically, new files are placed on the disks with the most (absolute) free space. that means that:

Once the 8TB drives are 2TBs filled, the pool will start to use the 6TB drives.

Once the 8TB drives are 3TBs filled AND the 6TB drive is 1TB filled, it will start to use the 5TB drives.

Once the 8TB drives are 7TBs filled, AND the 6TB drive is 5TB filled, AND the 5TB drives are 4TB filled, it will ONLY then start to use the 1TB drive.



Certain... well, actually, all of the optional balancers change this behavior.

  • The SSD Optimizer places new files on the "feeder/SSD" disks and then to the other disks... but uses the same strategy, unless you use the "Ordered File Placement" option (don't use the SSD Optimizer and Ordered File Placement balancer at the same time, as there is an issue with that).
  • The "Ordered File Placement" balancer completely changes this behavior. It fills up one (or two or more, depending on duplication) disk(s) at a time. Once the disk is ~90% full (IIRC), it moves to the next disk, filling that up. The order of the disks is specified in the balancer.
  • The "Disk Space Equalizer" forces the pool to fill the disks equally, based on percentage, or size (your choice). 

you can download any or all of them from here:


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I have 2 8TB Drives in a pool with "File Pool Duplication" turned on.


But I am not getting a Mirror of the data between the drives.


How do I get the Mirror created? Folder duplication has 2x on all folders.





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Basically, patience. Just let it sit and run.


Specifically, see at the bottom, where it says "Duplicating... (9.8%)"? This indicates that the software is actively copying the unduplicated data to the other drive. Since this is approximately 3TBs of data... that will take a while.  


Normally, it takes roughly 4 hours per TB to copy the data. That means in ideal circumstances, it may take about 12 hours to copy all of the data on your pool to the other drives.   

However, the duplication process runs at a lower priority, so this may actually take a lot longer to complete. If you click on the ">>" arrows at the bottom, this boosts the priority of the duplication task, but at the expense of overall pool performance. 

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