XFS File System Overview

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XFS is a highly scalable, high-performance file system which was originally designed at Silicon Graphics, Inc. XFS is the default file system for Red Hat Enterprise Linux 7.

Main Features

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 7 supports backup and restore utilities specific to XFS.

Allocation Features

XFS features the following allocation schemes:

  • Extent-based allocation
  • Stripe-aware allocation policies
  • Delayed allocation
  • Space pre-allocation

Delayed allocation and other performance optimizations affect XFS the same way that they do ext4. Namely, a program’s writes to an XFS file system are not guaranteed to be on-disk unless the program issues an fsync() call afterwards.

NOTE

Creating or expanding files occasionally fails with an unexpected ENOSPC write failure even though the disk space appears to be sufficient. This is due to XFS’s performance-oriented design. In practice, it does not become a problem since it only occurs if remaining space is only a few blocks.

Other XFS Features

The XFS file system also supports the following:

Extended attributes (xattr)

This allows the system to associate several additional name/value pairs per file. It is enabled by default.

Quota journaling

This avoids the need for lengthy quota consistency checks after a crash.

Project/directory quotas

This allows quota restrictions over a directory tree.

Subsecond timestamps

This allows timestamps to go to the subsecond.

Default atime behavior is relatime

Relatime is on by default for XFS. It has almost no overhead compared to noatime while still maintaining sane atime values.

 

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