Unfortunately not:
rhellwig@boejuniper6> show system snapshot
Non-recovery snapshots:
Snapshot snap.20190103.112901:
Location: /packages/sets/snap.20190103.112901
Creation date: Jan 3 11:29:01 2019
Junos version: 17.1R1.8
Snapshot snap.20190104.101954:
Location: /packages/sets/snap.20190104.101954
Creation date: Jan 4 10:19:54 2019
Junos version: 18.3R1.9
Total non-recovery snapshots: 2
Recovery Snapshots:
Snapshots available on the OAM volume:
recovery.ufs
Date created: Thu Jan 3 11:27:16 CET 2019
Junos version: 17.1R1.8
Total recovery snapshots: 1
{master}
rhellwig@boejuniper6> request system storage cleanup
List of files to delete:
Size Date Name
11B Jan 4 13:41 /var/jail/tmp/alarmd.ts
....
0B Jan 4 10:18 /var/tmp/rtsdb/if-rtsdb
Delete these files ? [yes,no] (no) yes
{master}
rhellwig@boejuniper6> request system snapshot recovery
Creating image ...
Compressing image ...
Image size is 2459MB
ERROR: The OAM volume is too small to store a snapshot
In the meantime I upgraded the SW to an actual level (18.3R1.9) but this didn't help.
On the second RE I also tried the request system recover oam-volume oper cmd as described in Software Installation and Upgrade Guide (p.503), but this went wrong and made the /oam unavailable...
rhellwig@boejuniper6> show system snapshot
Non-recovery snapshots:
Snapshot snap.20190103.143713:
Location: /packages/sets/snap.20190103.143713
Creation date: Jan 3 14:37:13 2019
Junos version: 17.2R3.4
Snapshot snap.20190104.100147:
Location: /packages/sets/snap.20190104.100147
Creation date: Jan 4 10:01:47 2019
Junos version: 18.3R1.9
Total non-recovery snapshots: 2
Recovery Snapshots:
mount: /dev/oam: No such file or directory
Reboot, offline/online and upgrade didn't solve this 2nd problem.