3.9. Relatime Drive Access Optimization
The POSIX standard requires that operating systems maintain file system metadata that records when each file was last accessed. This timestamp is called
atime, and maintaining it requires a constant series of write operations to storage. These writes keep storage devices and their links busy and powered up. Since few applications make use of the
atimedata, this storage device activity wastes power. Significantly, the write to storage would occur even if the file was not read from storage, but from cache. For some time, the Linux kernel has supported a
noatimeoption for mount and would not write
atimedata to file systems mounted with this option. However, simply turning off this feature is problematic because some applications rely on
atimedata and will fail if it is not available.
The kernel used in Red Hat Enterprise Linux 7 supports another alternative —
atimedata, but not for each time that a file is accessed. With this option enabled,
atimedata is written to the disk only if the file has been modified since the
atimedata was last updated (
mtime), or if the file was last accessed more than a certain length of time ago (by default, one day).
By default, all filesystems are now mounted with
relatimeenabled. You can suppress it for any particular file system by mounting that file system with the option