Losing files after removing drive from mergerfs pool

Hello forum!

I am experiencing a very unusual issue that I cannot explain myself. First, my configuration:

1. x4 1 TB hard drives

2. x3 hard drives are pooled together with mergerfs

3. The fourth hard drive works as parity for snapraid

4. All my shared folders (namely samba shares) are spread across the pool, which is evenly distributed (all 3 drives are similarly full)

I wanted to remove one of the drives out of the pool, not from the system, only from the pool. So, I did the following:

1. In OMV UI, I removed the drive (lets call it solo-drive) from the pool. The name of the pool remained the same, but it has only 2 drives now.

2. Log in via SSH, and using MC copy the files from the solo-drive to the pool

3. I did not restarted my system in between

The problem is that the transfer of files went bananas: I first copied a folder with non-critical data. For that I just moved the files from the solo-drive to the pool. Moving the data went fine, but when it was finished it disappeared from both the solo-drive AND the pool. I then tried coping first and then deleting from the solo-drive, with the same result. In short, deleting a folder from the solo-drive deletes also its equivalent in the pool. For whatever reason, although the solo-drive is no longer in the pool, the files inside are still somehow linked.

So, I decided to stop before moving my critical files. Any idea why this is happening?

Replying to myself, I found a solution with the help of Reddit. Tl;DR: OMV does not apply the changes from MergerFS on the fly, meaning that the drive pool must be remounted after any changes are done (restarting OMV also works). Therefore, although the Web interface shows the that the pool is only composed of two drives instead of three, the underlying OS has not applied the changes yet. Hence, any changes done to the files in the non-pooled drive will be reflected in the pooled drives.

After mod fing the pool and restarting the system I was able to modify the files in the pooled drive without affecting the ones in the pooled ones.

Zitat von ryecoaaron

Nope. This is why the restart button (which should remount) is there. I don't like the idea of restarting the pool with any change because something may be using it.

As a safety measure, I believe a manual restart of the pool is the way to go. In that case you can avoid unintentional changes to the pool. The mistake was on my side, since I ignored that a restart of the pool is necessary to apply the changes. That is not a problem with OMV, that is simply how MergerFS works.