[Asus Zenfone 5Z  ROMs, Kernels, Recoveries, & Othe] wstephen:
Backup & Restore Procedures

Thank you for sharing this idea - it may be the designed/desirable feature to have TWRP and Operating System to be installed on different slots.

If this is the idea, it would mean that the proper Nandroid Backup procedure should be:

1) adb reboot-bootloader while in the operating system or, power-off then goto bootloader;

2) Swap to the Inactive Slot where TWRP resides;

3) Reboot into TWRP using the Bootloader's Menu;

4) Swap to the slot using TWRP's "Set Active Slot" tool to where the operating system was installed (or we call it system slot)

5) Make a Nandroid Backup with the TWRP Backup Function.

This procedure involves slot swapping twice. And after finishing the Nandroid Backup, you may directly get back to your operating system using the TWRP's "Reboot to System" because you are already on the "System Slot" at time when you were carrying out your Nandroid Backup. Notice: This backup would not include the TWRP itself.

However, this procedure does not appear to be in tie with Post #2 where [MENTION=5216756]jackeagle[/MENTION] mentioned - "Warning: DO NOT SWITCH SLOTS USING TWRP SETTINGS FOR NOW! USE FASTBOOT METHOD ITSELF ELSE YOU WONT BE ABLE TO BOOT STOCK!" as if it were the designed deployment procedure anticipated by jackeagle though we have tested Switching Slot by TWRP Settings would not actually result in any unexpected problem.

I wish someone who has tested the complete Backup & Restore Process with this version of TWRP may be kind enough to help us by sharing their hands-on experience.

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Follow UP Tests

I, eventually, tested Backup Procedure mentioned above. And here's the results:

1) Obviously, I can freely change slot from A (where the TWRP resides) to B (where Operating System resides) and, the TWRP does accurately indicate which slot is being the Current Slot.

2) After swapping to Slot B with TWRP interface, I appeared to be able to backup all the partitions, but I've chosen to leave out the system.img and vender.img partitions (to save time).

3) The date attached to the Backup Folder was wrong because the TWRP in Slot A was not able to sync that date information from the Operating System that was installed in Slot B. There are contents in the backup folder as well.

4) I, then, wiped the System Partition on Slot B using Advanced Wiping. And then, followed up by restoring my System Partition using TWRP Backup just generated. The restore process looked fine on the TWRP interface.

5) Since my active slot was on B at time of the Backup, so I tried to reboot directly to System from the TWRP's "Reboot to System".

6) I ended up rebooted to the Bootloader. From the Bootloader menu, I selected "Power Off".

7) I attempted to cold boot by just pressing the Power Button, but I've got booted into Bootloader again.

8) I went to TWRP by changing to Slot A, then install system.img (extracted from Stock Rom) into Slot B.

9) I rebooted to System with active slot set to Slot B, my device is working normally again.

To conclude, other than flashing images and zip, I do not think this version of TWRP is ready for Nandroid Backup & Restore deployment yet. However, I am thankful for [MENTION=5216756]jackeagle[/MENTION] 's effort so far.