I have the following question that basically is not answered clearly by any documentation)
Scenario: upgrade mx80 from JUNOS 16.1R5-7 to 18.4R3.I want to go for the following upgrade-path:
Start sw version installed: JUNOS 16.1R5-7Intermediate sw version: 17.2R3.4Intermediate sw version: 18.1R2.6Final sw version: 18.4R3
Now in case of problem I want to use only the so called "snapshot":"On routers running Junos OS, back up the currently running and active file system partitions to standby partitions that are not running."
I already run the snapshot and now on the Internal NAND flash device (da1) there is a backup of root file system and of /config.
user@mx-80> request system snapshotVerifying compatibility of destination media partitions...Running newfs (899MB) on internal media / partition (da1s1a)...Running newfs (100MB) on internal media /config partition (da1s1e)...Copying '/dev/da0s1a' to '/dev/da1s1a' .. (this may take a few minutes)Copying '/dev/da0s1e' to '/dev/da1s1e' .. (this may take a few minutes)
The following filesystems were archived: / /config
What was copied?
user@mx-80> show system snapshotInformation for snapshot on internal (da1s1)Creation date: Apr 22 10:35:33 2020JUNOS version on snapshot:jbase : ppc-17.2R3.4jcrypto: ppc-17.2R3.4jcrypto-dp-support: 17.2R3.4jdocs : 17.2R3.4jkernel: ppc-17.2R3.4jmacsec: 17.2R3.4jpfe : MX80-17.2R3.4jroute : ppc-17.2R3.4jsd : powerpc-17.2R3.4jsdn-powerpc: 17.2R3.4jweb : ppc-17.2R3.4py-base-powerpc: 17.2R3.4py-extensions-powerpc: 17.2R3.4
Assuming that during the upgrade the router will not boot-up from da0 (does not matter in which step i am on the above upgrade path) and assuming that i do not want to use any usb, than the last chance for the router to boot-up is to use the da1.Question: did i get correctly that in this case the router, using the snapshot on da1, will restore the OS 17.2R3.4 plus the configuration that was saved?
The snaptshot allows you to copy/backup the JunosOS file system to the backup partition. In case the primary gets corrupted for some reason, the router will bootup from the secondary, so that you can continue working. Now every time you perform an upgrade, you will need to take the snaptshot so they sync, otherwise in your example, let's say you took the snapshot at 17X and you already upgraded to 18 but you didn't take the snaptshot; If the primary partition fails to boot the router will go to the 17 as this is where you took the snapshot.
So, to answer your question. Yes, If primary partition fails, the router will bootup with the backup partition and will restore the OS 17.2R3.4 plus the configuration that was saved.