7.3.2. The XFS File System

XFS is a robust and highly-scalable single host 64-bit journaling file system. It is entirely extent-based, so it supports very large file and file system sizes. The maximum supported file system size in Red Hat Enterprise Linux 6.8 and later is 300 TB. The maximum supported XFS file system size in Red Hat Enterprise Linux 6.7 and earlier is 100 TB. The number of files an XFS system can hold is limited only by the space available in the file system.

XFS supports metadata journaling, which facilitates quicker crash recovery. The XFS file system can also be defragmented and enlarged while mounted and active. In addition, Red Hat Enterprise Linux 6 supports backup and restore utilities specific to XFS.

XFS uses extent-based allocation, and features a number of allocation schemes such as delayed allocation and explicit pre-allocation. Extent-based allocation provides a more compact and efficient method of tracking used space in a file system, and improves large file performance by reducing fragmentation and the space consumed by metadata. Delayed allocation improves the chance that a file will be written in a contiguous group of blocks, reducing fragmentation and improving performance. Pre-allocation can be used to prevent fragmentation entirely in cases where the application knows the amount of data it needs to write ahead of time.

XFS provides excellent I/O scalability by using b-trees to index all user data and metadata. Object counts grow as all operations on indexes inherit the logarithmic scalability characteristics of the underlying b-trees. Some of the tuning options XFS provides at mkfs time vary the width of the b-trees, which changes the scalability characteristics of different subsystems.