[DSM 7 + External HDDs detected as internal HDD]

I also tried this: 

 

https://www.casler.org/wordpress/synology-ssd-cache-on-external-devices/

 

 

[DSM 7 + External HDDs detected as internal HDD]

Hi guys, 

 

I've a DS1621+ NAS but my volume is ext4 (27 To of data) so I can't migrate it to btrfs file system.

My goal is to be able to use Virtual Manager (only works with btrfs).

 

I found some tuto here but none of them works for me:

Eg: 

 

I'd like to use an external BTRFS USB drive for Vitual Manager, so I need to have this drive detected as internal...

 

Any help will be appriciate. 

Thx