mobile

Hi guys,
I am getting interested in these ROM flashing things recently, so I backed up /System /Data /Boot by TWRP after I installed all apps I want.
Just today, I tried to restore from one of my backups but couldn't get it work. CM12 just stuck on the boot animation screen forever.
The backup & restore processes were all perfect without any error, the MD5 also matched.
Here are some basic facts I made:
1. I wiped /System /Data /Cache /D-Cache before restoring.
2. I wiped /Cache /D-Cache after restoring.
3. Reflasing kernel -> NO change
4. Reflashing /System /GApps -> NO change
5. Fix Permission ->NO change
6 Wipe /Data = CAN boot
So clearly there is something wrong with /Data.
I'm thinking the f2fs /data just can' be restored by TWRP? but I couldn't find such information on the web.
Can anyone confirm this?
Thanks!

[Spec]
Nexus 7 2013 WIFI(flo)
TWRP 2.8.6
Kernel Glitch for Flo/Deb - r320
(No overlock, No additional drivers)
CM12 Nightly 20150405
gapps itvends.com/gapps/gapps-lp-20141212-signed.zip
/Data /Cache=f2fs
/System = ext4