With btrfs, it's possible to resize the btrfs filesystem when it is online and is being accessed by users. The size of a filesystem will grow automatically if we add or remove devices; we will see this in the next subsection of this chapter; however; we can resize the filesystem should we need to even on a single device that we have created. Using the following command, we will shrink the assigned space to the filesystem by 500MiB:

# btrfs filesystem resize -500m /data/simple

If we check the size of the filesystem before and after, we can see the dynamic change that takes place: