Yesterday I decided to finally reinstall or restore the system.
Turned out to be a pretty horrendous experince, but at least it can help someone who'll decide to do the same
Some parts of it might only be applicable to older hardware, in my case a 2012 Macbook Retina.
What I found out
1) Recovery partition contains High Sierra (good)
2) Internet Recovery started when this partition is not present starts Lion installation (that will depend on what your HW shipped with)
3) Internet Recovery when invoked manually starts Sierra Installation
4) Time Machine backups made on 10.13 don't work with Sierra Time Machine (they do, mostly, but not for restoring the whole system)
5) Deleting your OS APFS Volume will not reclaim any significiant disk space!!!
6) Choosing "Restore from Time Machine" will thus not free anything and will run out of space shortly after starting restore!
What does it all mean?
Well, the only way to reclaim this lost disk space is to recreate the APFS Container, even deleting the whole volume doesn't free anything. Take a look how it looked after deleting disk2s1, AKA my root volume:
APFS Container (1 found)
|
+-- Container disk2 FD4007F5-FE7F-4DE9-B21A-941F76189504
====================================================
APFS Container Reference: disk2
Capacity Ceiling (Size): 479238864896 B (479.2 GB)
Capacity In Use By Volumes: 465694814208 B (465.7 GB) (97.2% used)
Capacity Available: 13544050688 B (13.5 GB) (2.8% free)
|
+-< Physical Store disk0s2 00000064-76DA-0000-5C45-000096220000
| -----------------------------------------------------------
| APFS Physical Store Disk: disk0s2
| Size: 479238864896 B (479.2 GB)
|
+-> Volume disk2s2 27355FD9-0817-4AF5-8D42-81115A5CC7C1
| ---------------------------------------------------
| APFS Volume Disk (Role): disk2s2 (Preboot)
| Name: Preboot
| Mount Point: Not Mounted
| Capacity Consumed: 30117888 B (30.1 MB)
| Capacity Reserve: None
| Capacity Quota: None
| Encrypted: No
|
+-> Volume disk2s3 0CA2FD60-F37B-4D46-A91A-CCAFA36C10EB
| ---------------------------------------------------
| APFS Volume Disk (Role): disk2s3 (Recovery)
| Name: Recovery
| Mount Point: Not Mounted
| Capacity Consumed: 2581450752 B (2.6 GB)
| Capacity Reserve: None
| Capacity Quota: None
| Encrypted: No
|
+-> Volume disk2s4 518E1584-3568-43DB-9673-43003ED70192
---------------------------------------------------
APFS Volume Disk (Role): disk2s4 (VM)
Name: VM
Mount Point: Not Mounted
Capacity Consumed: 1073766400 B (1.1 GB)
Capacity Reserve: None
Capacity Quota: None
Encrypted: No
And yes, fsck was still pretty happy with this situation. Nothing wrong here, move along...
Also, after deleting this Volume, even though Recovery Volume was still present, Macbook would no longer boot Recovery anymore. That means you're stuck with Sierra (hopefully) which will not restore your High Sierra installation, thus you either need to revert to a Sierra backup (that's what I did) or somehow boot the installer (from USB stick?) and delete and recreate the whole Container.
But even if you solve this, for some reason contents of the other Volumes simply can't be dumped and restored - you'll get a permission denied. I'm sure this could be solved but I haven't had a chance to try.
Apple really needs to provide a working fsck_apfs to fix this in the first place. It's pretty sad that the one we have can't really be used from Recovery anyway and even this wasn't fixed in the second Beta. Even for a development machine, having no way to even restore system from this state makes it absolutely unacceptable to install IMO. Tools such as fsck simply can't be left for "later" just because it's not meant to be public yet...
If only Apple went with ZFS instead of reinventing the wheel...