XFS
High-performance journaling filesystem. SGI 1994 (for IRIX). Port to Linux 2001. Default on RHEL 7+ desktop + server. Excellent for large files + high concurrency (databases, scientific computing).
B+ tree-indexed metadata → fast directory lookups even with millions of files per directory. Delayed allocation → better placement minus fragmentation. Online resize (only grow, not shrink). Quota support. Modern improvement: reflink support (since kernel 4.16) for CoW-like snapshots without ZFS/Btrfs. Standard choice for PostgreSQL deployments — ext4 is fine-tuned-okay but XFS scales better on 100+ core systems. RHEL trend: XFS as default filesystem for / and /home; Btrfs as experimental option.