How do I find on which physical device a folder is located?

The df(1) command will tell you the device that a file or directory is on:

df /work 

The first field has the device that the file or directory is on.

e.g.

$ df /root Filesystem 1K-blocks Used Available Use% Mounted on /dev/sda1 1043289 194300 795977 20% / 

If the device is a logical volume, you will need to determine which block device(s) the logical volume is on. For this, you can use the lvs(8) command:

# df /usr Filesystem 1K-blocks Used Available Use% Mounted on /dev/mapper/orthanc-usr 8256952 4578000 3259524 59% /usr # lvs -o +devices /dev/mapper/orthanc-usr LV VG Attr LSize Origin Snap% Move Log Copy% Convert Devices usr orthanc -wi-ao 8.00g /dev/sda3(0) 

The last column tells you that the logical volume usr in the volume group orthanc (/dev/mapper/orthanc-usr) is on the device /dev/sda3. Since a volume group can span multiple physical volumes, you may find that you have multiple devices listed.

Another type of logical block device is a md (Multiple Devices, and used to be called meta-disk I think) device, such as /dev/md2. To look at the components of a md device, you can use mdadm --detail or look in /proc/mdstat

# df /srv Filesystem 1K-blocks Used Available Use% Mounted on /dev/md2 956626436 199340344 757286092 21% /srv # mdadm --detail /dev/md2 ...details elided... Number Major Minor RaidDevice State 0 8 3 0 active sync /dev/sda3 1 8 19 1 active sync /dev/sdb3 

You can see that /dev/md2 is on the /dev/sda3 and /dev/sdb3 devices.

There are other methods that block devices can be nested (fuse, loopback filesystems) that will have their own methods for determining the underlying block device, and you can even nest multiple layers so you have to work your way down. You'll have to take each case as it comes.

For a script, you can use:

$ df -P <pathname> | awk 'END{print $1}' 

This is POSIX compatible.

In modern distributions of Ubuntu there's an additional layer (device mapper) between your file/directory and the device. /dev/mapper contains symbolic links pointing to the actual special devices. For example, trying on the current directory:

$ df . | grep '^/' | cut -d' ' -f1 /dev/mapper/kubuntu--vg-root $ ls -l /dev/mapper/kubuntu--vg-root lrwxrwxrwx 1 root root 7 Nov 22 18:02 /dev/mapper/kubuntu--vg-root -> ../dm-1 

So to get the full path of device programmatically, you can use:

$ realpath $(df . | grep '^/' | cut -d' ' -f1) 

Which is my case prints:

/dev/dm-1 

realpath is part of GNU coreutils.

$ findmnt -no source -T / # mountpoint /dev/nvme0n1p2 $ findmnt -no source -T /usr # directory under mountpoint /dev/nvme0n1p2 $ COLUMNS=70 man findmnt | sed -E '/^ {7}-[noT]/,/^$/!d;s/^ {7}//' -n, --noheadings Do not print a header line. -o, --output list Define output columns. See the --help output to get a list of the currently supported columns. The TARGET column contains tree formatting if the --list or --raw options are not specified. -T, --target path Define the mount target. If path is not a mountpoint file or directory, then findmnt checks the path elements in reverse order to get the mountpoint (this feature is supported only when searching in kernel files and unsupported for --fstab). It’s recommended to use the option --mountpoint when checks of path elements are unwanted and path is a strictly specified mountpoint.