Hello
From the article we can see that in the new junos we have 2 type of snapshots.
The one you are looking for is the recovery snapshot
root@EX34xx> request system snapshot recovery
fpc0:
--------------------------------------------------------------------------
Creating image ...
Compressing image ...
Image size is 243MB
Recovery snapshot created successfully
Recovery snapshot does the same thing as request system snapshot slice alternate
on the older platforms.
So if you do the recovery snapshot after the upgrade then you can recover the junos from the OAM volume as follows
root@EX3400> request system recover oam-volume
NOTICE: Recovering the OAM volume ...
da0p1 deleted
da0p1 added
/dev/gpt/oam: 500.0MB (1024000 sectors) block size 32768, fragment size 4096
using 4 cylinder groups of 125.03MB, 4001 blks, 16128 inodes.
super-block backups (for fsck_ffs -b #) at:
192, 256256, 512320, 768384
Verified oam signed by PackageProductionEc_2016 method ECDSA256+SHA256
Installing OAM volume contents ...
The OAM volume is now installed
NOTICE: Creating a recovery snapshot on the OAM volume ...
Creating image ...
Compressing image ...
Image size is 243MB
Recovery snapshot created successfully
NOTICE: OAM volume recovered >>> Recovered