I have not used XFS - the information here is simply a (brief) precis of the various man pages on the subject.
XFS combines advanced journalling technology with full 64-bit addressing and scalable structures and algorithms.
An XFS filesystem can reside on a regular disk partition or on a logical volume.
A file system can be made up of up to three parts/sections:
- a data section
- a log section
- a realtime section
The default 'mkfs.xfs' behavior does NOT create the realtime section and the log area is contained within the data section. The log section, therefore, can be either separate from the data section or contained within it.
The filesystem sections are divided into a number of blocks the size of which can be specified using the '-b' option to 'mkfs.xfs'.
Each XFS filesystem is labeled with a Universal Unique Identifier (UUID). The UUID is stored in every allocation group header and is used to help distinguish one XFS filesystem from another, therefore you should avoid using 'dd' or other block-by-block copying programs to copy XFS filesystems. If two XFS filesystems on the same machine have the same UUID, 'xfsdump' may become confused when doing incremental and resumed dumps.
'xfsdump' and 'xfsrestore' are recommended for making copies of XFS filesystems.
- The data section
Contains all the filesystem metadata (inodes, directories, indirect blocks) as well as the user file data for ordinary (non-realtime) files and the log area if the log is internal to the data section.
- The log section
(or area, if it is internal to the data section) is used to store changes to filesystem metadata while the filesystem is running until those changes are made to the data section. It is written sequentially during normal operation and read only during mount. When mounting a filesystem after a crash, the log is read to complete operations that were in progress at the time of the crash.
- The realtime section
Is used to store the data of realtime files. These files have an attribute bit set through xfsctl after file creation, before any data was written to the file.