EXT4 – The file system uses a function called journaling. Journaling, in short, is a file system log. What this provides to you as the user is a quick method of recovery if there is ever a system failure: unclean shutdown, file corruption, etc. If there is ever a problem, the journal is called and the data is restored with no issues. The cost of this journaling feature, however, is CPU time/usage. CPU cycles are used to write the journal to the disk.
EXT2 – This file system does not use journal. No recovery method, etc. So if something is corrupted, there is no way to recover corrupted files/blocks/data.
What does all of this mean? – Simple. What it means is those of us who are rooted, running a stable ROM/Kernel combo, and using a backup method such as TWRP or CWM, can safely use EXT2 for /system without any worry because all we need to do is make a backup of our /system partition via recovery, tuck it away on our internal SD card and save it for a rainy day - restore it if there is every an unclean shutdown (battery pull, reboot caused by an unstable kernel, etc.).
What benefits will you see/feel?
Honestly, I have no idea at this point. I know for a fact that the device will boot faster and read operations on the /system partition will be absolutely insanely fast. As fast as they can possibly be on the Note 3. As far as “end of the day” battery savings, well, this is kind of the point of me doing this and sharing. I am going to find out, and post my results here so other people can decide if they do or don’t want to do this as well. If all goes well, I’ll edit this post tomorrow with some quick instruction on how to convert the file system. It should be a quick and easy process.
Other benefits of using EXT2 instead of EXT4:
EXT2 is backward compatible with EXT4. What this means is you can have a file system formatted to EXT2, and it can be mounted as EXT4 and it will only utilize the newer useful features found in EXT4 that were not originally present when EXT2 was introduced. When mounted as EXT4, EXT2 will not use journaling, but will use EXT4’s superior block allocation and “tagging” feature. EXT4 has the ability to mark unused blocks on the disk so it knows to not look there for data – this saves precious time in read operations. EXT2 does not have this feature… except when it is mounted as EXT4
The biggest advantage, here, is to get rid of that useless EXT4 journaling feature used on our RO /system and save CPU cycles. We use backups.We are a different breed of users, right? We demand performance and push our devices to the limits and somehow manage to maintain a stable and usable system, correct?
YES! So, we’re gonna go ahead and take advantage of this super awesome backward compatibility of EXT2 on the /system partition and get some positive performance index out of it
INSTRUCTIONS - convert /system to EXT2
1. Unzip the .zip folder of your ROM of choice.
2. Find /META-INF/com/google/android/updater script.
3. Open the updater-script file in a text editor.
Any lines where you see "EXT4" and "system" in the same line, you need to change that 4 to a 2. Only do this for lines with system and EXT4 in the same line.
4. Save the changes, then zip the ROM back up.
5. Place ROM on your internal SD card, then boot into recovery - YOU MUST BE USING TWRP FOR THIS
6. Once you get into recovery, you will see your TWRP options (there are 8 tiles in recovery) - select the one that says "Advanced"
7. You will now see 6 tiles. On the left side, select the one that says "Terminal Command"
8. At the top you should see a / symbol - this is the directory you are going to begin your session in. You want it to be /
9. On the bottom right of the screen, hit "Select"
This next part is very important. Do not mess up.
When you get to the terminal screen, type this command:
mke2fs /dev/block/mmcblk0p23 DO NOT continue until you have double checked that the number you punched in is 23! I cannot stress this enough. 23.... 23..... 23..... again that last part is "...mmcblk0p23"
After it finishes reformatting, flash your ROM of choice (the one where you edited any lines). When you are done, boot up.
You are now running an EXT2 file system for your /system partition. Welcome to the thunder dome