макет, параметры монтирования и поддерживаемые атрибуты файлов для файловой системы XFS (layout, mount options, and supported file attributes for the XFS filesystem)
Описание (Description)
An XFS filesystem can reside on a regular disk partition or on a
logical volume. An XFS filesystem has up to three parts: a data
section, a log section, and a realtime section. Using the
default mkfs.xfs(8) options, the realtime section is absent, and
the log area is contained within the data section. The log
section can be either separate from the data section or contained
within it. The filesystem sections are divided into a certain
number of blocks, whose size is specified at mkfs.xfs(8) time
with the -b option.
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 data section is divided into a
number of allocation groups. The number and size of the
allocation groups are chosen by mkfs.xfs(8) so that there is
normally a small number of equal-sized groups. The number of
allocation groups controls the amount of parallelism available in
file and block allocation. It should be increased from the
default if there is sufficient memory and a lot of allocation
activity. The number of allocation groups should not be set very
high, since this can cause large amounts of CPU time to be used
by the filesystem, especially when the filesystem is nearly full.
More allocation groups are added (of the original size) when
xfs_growfs(8) is run.
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 had an attribute bit set through xfsctl(3) after file
creation, before any data was written to the file. The realtime
section is divided into a number of extents of fixed size
(specified at mkfs.xfs(8) time). Each file in the realtime
section has an extent size that is a multiple of the realtime
section extent size.
Each allocation group contains several data structures. The
first sector contains the superblock. For allocation groups
after the first, the superblock is just a copy and is not updated
after mkfs.xfs(8). The next three sectors contain information
for block and inode allocation within the allocation group. Also
contained within each allocation group are data structures to
locate free blocks and inodes; these are located through the
header structures.
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(1) or other block-by-block
copying programs to copy XFS filesystems. If two XFS filesystems
on the same machine have the same UUID, xfsdump(8) may become
confused when doing incremental and resumed dumps. xfsdump(8)
and xfsrestore(8) are recommended for making copies of XFS
filesystems.
