HowTo Disable The "relatime" Method For File "atime" Updates

Overview

This "HowTo" explains various ways to disable the "relatime" method in the Linux Kernel for updating the "atime" field for a file when a process "read" occurs. One should consider only disabling the "relatime" method for audit or debugging purposes. A significant disk I/O performance hit may occur for an active Linux server if this method is disabled.

atime

The "Access time" field for a file within a given file system is know as: "atime". When a process reads a file, the "atime" field is updated with the current date/time for this access. Completely disabling "atime" updates using the "noatime" mount flag is probably one of the biggest performance tweaks that a Linux administrator can make. An active Linux server is continually reading files which generates a significant number of "atime" updates. This translates to numerous metadata updates made to the file system by writes to the physical disk which can lead to poor I/O performance.

relatime

The Linux Kernel supports the "Relative atime" (relatime) update method. A "relatime" update will only updated the "atime" field if the previous "atime" is older than the "mtime" (modify time) or "ctime" (change status time) for the file. This technique can avoid a significant number of metadata "atime" updates. It's similar to the "noatime" mount option, but useful for applications like "mutt" that need to know when a file has been read since it was last modified.

NST has the "relatime" Kernel option enabled by default.