Tools
Inode capacity for ext4, XFS, ZFS and other filesystems.
An inode is metadata for every file and directory. Running out of inodes yields “no space left” while the disk still has bytes — common with millions of small files.
ext4 defaults to roughly one inode per 16 KB. XFS and ZFS use different ratios. The result is an estimate; mkfs options change reality.
Containers and maildir workloads with millions of tiny files run out of inodes before gigabytes. After format, the ratio only changes with a new mkfs.
df -i. At 100%, delete files, move to a larger FS, or reformat with a different ratio.
XFS allocates inodes as needed; it is not ext4’s “all up front” model. The estimate is still rough.
ext4 mkfs -i. Lower for many small files (more inodes), higher for large files.
Layers and overlay create many files. Watch df -i on the container host.
No. mkfs options, snapshots and copies change reality.