[Nexus 6P Android Development] DanJayF:
Successfully switch to F2FS & keep your current setup

Right so I thought I'd post my complete method on switching to F2FS since a lot of people seem to be having problems. I worked for 6 hours yesterday on this and finally found a way to make it work while successfully restoring my EXT4 Data partition.

I worked off this post by [MENTION=5351947]Iceburn1[/MENTION] for the most part to clean install my ROM first. Thanks man!

What I used:

PureNexus ROM

Full Dynamic Gapps

SuperSU Beta

Flash Kernal

Flash's TWRP

Method to switch to F2FS while keeping your current setup:

If using any screen security such as pattern/PIN lock, disable it first (optional but HIGHLY recommended to prevent issues during restore).

Download the latest TWRP F2FS by [MENTION=6842057]The Flash[/MENTION]. Then in your bootloader "fastboot flash recovery" the new TWRP img file.

Boot into TWRP.

Choose Backup > Data, and let it run. Then transfer the TWRP/BACKUPS folder to your computer as the local backup will be wiped!! (OPTIONAL: I chose to backup everything except the system and vendor images in case I needed to do a full restore.)

Manually backup and transfer any folders in Internal Storage that you need to your computer as these will be wiped also!

In TWRP choose Wipe > Advanced Wipe > Dalvik / ART Cache, System, Data, Cache > Swipe to Wipe.

Go back to Wipe > Format Data > type "yes" and continue.

Wipe > Advanced Wipe > choose Data > Repair or Change File System > Change File System > F2FS > Swipe to change

Wipe > Advanced Wipe > choose Cache > Repair or Change File System > Change File System > F2FS > Swipe to change

Reboot into recovery and choose Wipe > Advanced > Data > Repair or Change... and make sure it says "File System: f2fs". Do the same with Cache to double check it has stuck.

Transfer all the ZIPs you intend to flash (ROM, Gapps, Kernel etc.)

If your ROM requires to flash a Vendor Image, flash it now.

Flash an F2FS compatible ROM (Such as PureNexus)

Flash GApps (I used Full Dynamic Gapps)

Flash any other mods you have such as SuperSU, Viper4Arise etc. (Optional)

Flash F2FS compatible Kernel (I used Flash Kernel)

Wipe Cache & Dalvik just in case.

Reboot system and wait for the Welcome screen to appear.

Then reboot into TWRP to make sure Data & Cache are still F2FS like in Step 10. (If data has changed back to EXT4 then see Other Tips below)

Now transfer over your TWRP/BACKUPS folder back to your phone, as well as any other Internal Storage folders you backed up.

IMPORTANT: Open TWRP Settings and make sure "Use rm -rf instead of formatting" is ON (Ticked), otherwise Data will be reformatted to EXT4 when restoring!

TWRP > Restore > select your backup folder > deselect everything except Data > Swipe to Restore. (Don't worry about the yellow warning about having to switch back to EXT4. It still worked for me using this method)

Reboot System & PROFIT

Other Tips:

If after Step 19 your Data partition has changed back to EXT4 (This happened to me the first time), then reboot to your bootloader and run the following commands from fastboot:

fastboot format system
fastboot format userdata
fastboot format cache

Now continue from Step 8 onwards...

It'll take a while to reboot the second time after data has been restored. Also everything for me seemed quite clunky and slow for the first 30 minutes as it readjusts itself, but after that normal operations really do speed up such as opening apps, loading web pages etc. It's not a huge difference but it is definitely noticeable.

Let me know if there's anything I should add or change above. Good luck!