Directory merge subpath for SSD and Spninning Disk

[tyjtyj]

I need some help understanding epmfs policy.

I have 3 drives ssd, mechA and mechB with dir path as below where mechA/B is spinning drive. I would like to fill up SSD with download and use mechA as backup increase ssd runs out of space. mechB will be backup of mechA incase mechA out of space
SSD 100GB free
/nasdisk/download
/folder1
/file1
MechA 4TB free
/nasdisk/folder1
/nasdisk/folder2
/nasdisk/folder3
/nasdisk/file1
/nasdisk/file2
/nasdisk/file3
MechB 2tb free
/nasdisk/folder11
/nasdisk/foldee12
/nasdisk/folder13
/nasdisk/file11
/nasdisk/file12
/nasdisk/file13

how should i mount it to avoid fillup SSD when creating files and folder on /nasdisk ?
is this the correct setting ?
/etc/fstab
/mnt/mechA:/mnt/ssd:/mnt/mechB /mnt/hdd fuse.mergerfs minfreespace=10G,cache.files=partial,dropcacheonclose=true,category.create=epmfs,x-systemd.mount-timeout=1min 0 0

or (not the position of /mnt/ssd)
/mnt/mechA:/mnt/mechB :/mnt/ssd /mnt/hdd fuse.mergerfs minfreespace=10G,cache.files=partial,dropcacheonclose=true,category.create=epmfs,x-systemd.mount-timeout=1min 0 0

[trapexit]

You can't use epmfs and do anything like that. If you want to prioritize the drives by order then just put them in the relevant order and use ff with minfreespace set accordingly.

[tyjtyj]

Thanks for reply.

If I proceed with
/mnt/mechA:/mnt/mechB:/mnt/ssd /mnt/hdd fuse.mergerfs minfreespace=10G,cache.files=partial,dropcacheonclose=true,category.create=epmfs,x-systemd.mount-timeout=1min 0 0

what happen when ssd filled up until 10GB free.. will it create a folder in /mnt/mechA/nasdisk/download?
I am ok to manually delete the folder /mnt/mechA/nasdisk/download and let it fall back to /mnt/ssd/nasdisk/download

[trapexit]

As I said empfs won't do what you want. If you want to always prioritize the ssd then you should put it first in the list and use ff create policy.

Don't think about creating directories. mergerfs policies choose the branch to work on and then the branch is copied as needed. Read the section in the docs about policies and find the combination that does what you're looking for.