Ext3: Why journal is better than ordered when data needs to be readfrom and written to disk at the same time

[Jidong Xiao]

Hi,

I see many literatures mentioned this, but I have never seen any one
explains it in detail.(Although this link exposed the original story:
http://lkml.indiana.edu/hypermail//linux/kernel/0107.1/0364.html)

"Journal mode: This mode is the slowest except when data needs to be
read from and written to disk at the same time where it outperform all
others mode."

Since this is counter-intuitive, I believe many people are not aware
about the root cause. Can any one kindly explain it so as to make it
more clear? Thank you!

Regards
Jidong
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