Disk Size Management in Linux

There are two methods for resizing an encrypted disk:

Online Resize Method—The filesystem remains mounted and the clear text path for the device remains accessible during this process for most configurations. On some systems, the filesystem may need to be unmounted for when expanding or decreasing the disk size. Online resize is available for LVM (Logical Volume Manager) volumes.

Important: Online resize is not available if Online Encryption is enabled on the LVM volume. If you are using Online Encryption, you must resize the volume while it unmounted and detached.
Offline Resize Method—The filesystem must be unmounted. That means the data will not be available during this procedure. Offline resize is available for LVM volumes, root and swap devices, and data partitions.

Root, swap, and data partitions can both be expanded as required. Root partitions, however, cannot be reduced in size because they cannot be unmounted. If you need to grow the file system, run "resize / growfs".