btrfs-progs/Documentation/ch-fs-limits.rst

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maximum file name length
255
maximum symlink target length
depends on the *nodesize* value, for 4KiB it's 3949 bytes, for larger nodesize
it's 4095 due to the system limit PATH_MAX
The symlink target may not be a valid path, ie. the path name components
can exceed the limits (NAME_MAX), there's no content validation at ``symlink(3)``
creation.
maximum number of inodes
2\ :sup:`64` but depends on the available metadata space as the inodes are created
dynamically
inode numbers
minimum number: 256 (for subvolumes), regular files and directories: 257
maximum file length
inherent limit of btrfs is 2\ :sup:`64` (16 EiB) but the linux VFS limit is 2\ :sup:`63` (8 EiB)
maximum number of subvolumes
the subvolume ids can go up to 2\ :sup:`64` but the number of actual subvolumes
depends on the available metadata space, the space consumed by all subvolume
metadata includes bookkeeping of shared extents can be large (MiB, GiB)
maximum number of hardlinks of a file in a directory
65536 when the *extref* feature is turned on during mkfs (default), roughly
100 otherwise
minimum filesystem size
the minimal size of each device depends on the *mixed-bg* feature, without that
(the default) it's about 109MiB, with mixed-bg it's is 16MiB