The manual for the 'barrier' mount option is:barrier=0 / barrier=1 This  disables  /  enables the use of write barriers in the jbd code.barrier=0  disables, barrier=1 enables (default). This also requires an IO stack which can support barriers, and if jbd gets an error on a barrier write, it will disable barriers again with a warning.  Write  barriers  enforce  proper  on-disk ordering  of  journal  commits,  making volatile disk write caches safe to use, at some performance penalty.  If your disks are battery-backed in one way or another, disabling barriers may safely improve performance.But I do not know what the sentence proper on-disk ordering of journal commits means.Suppose normal order -- journal 1,data 1; journal 2, data 2.Which of the following ordering results will happen if I set barrier=0?  journal 2, data 2; journal 1, data 1; data 1, journal 1; data 2, journal 2.
What does the 'barrier' mount flag mean in Linux?
linux;mount;ext4