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.
7.3.2.1. Basic tuning for XFS
In general, the default XFS format and mount options are optimal for most workloads; Red Hat recommends that the default values are used unless specific configuration changes are expected to benefit the workload of the file system. If software RAID is in use, the
mkfs.xfs command automatically configures itself with the correct stripe unit and width to align with the hardware. This may need to be manually configured if hardware RAID is in use.
The
inode64 mount option is highly recommended for multi-terabyte file systems, except where the file system is exported via NFS and legacy 32-bit NFS clients require access to the file system.
The
logbsize mount option is recommended for file systems that are modified frequently, or in bursts. The default value is MAX (32 KB, log stripe unit), and the maximum size is 256 KB. A value of 256 KB is recommended for file systems that undergo heavy modifications.
