Filesystems

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If you must extract and isolate additional storage from sda without the risk of data loss due to shrinking the primary drive which is never advised, then a safer approach would be to use fallocate to create a loop device.

fallocate is great for creating swap on systems but can also be used to great effect when partitioning is not an option.

First, create a mount point for the loop drive.

mkdir /NewDrive

Now, you can go ahead and create the loop device.

fallocate -l 5G NewStorage

The above command will create will create a file NewStorage with a file size of just under 5GB. You can confirm this with ls -h

Now that the storage is isolated rather than partitioned, you will need to create a filesystem with it.

mkfs.ext4 NewStorage

This will create a ext4 filesystem. Now, you can mount it to the directory created earlier.

mount NewStorage /NewDrive

Your lsblk command should now return something like this

lsblk 
NAME MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda    8:0    0 298.1G  0 disk
sda1   8:1    0 298.1G  0 part /
loop0  7:0    0     5G  0 loop /NewDrive

And that is it without the risk of data loss or need for shrinking.

To see all active loop devices in use on your system, you can use losetup

losetup
NAME       SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE
/dev/loop0         0      0         1  0 /path/TO/NewDrive