Take a walk through EXT4’s history, features, and optimal use, and learn how it differs from previous iterations of the EXT filesystem. - An introduction to Linux’s EXT4 filesystem

• EXT4 - How does it work?
  • ext3/ext4 is now the same ext4 driver in the kernel
  • extended attribute part of the inode (96 par defaut)

see also

• The order of files in your ext4 filesystem does not matter - the actual argument value the JVM receives is “/jars/*”, and in turn decides to be helpful, and expand the wildcard anyway using the readdir syscall.
  • overlayfs delegates readdir to the underlying filesystem
  • the underlying filesystem happened to be an ext4
  • ext4 readdir optimizes by caching the entries of a directory in a “hashed b-tree” with a specific “directory hash seed”
  • the directory hash seed changed with the node image patch update, causing the jar order in the classpath to change, causing an uncaught throwable leading to “stuck” application initialization