How to do an snapshot on QFX5110

Hi all !

I would like to do a snapshot on QFX5110 , but the command request system snapshot do not appear on the CLI, neither using an USB as this link mentions : 

https://www.juniper.net/documentation/en_US/junos/topics/topic-map/backing-up-install-using-snapshot.html#id-creating-a-snapshot-and-using-it-to-boot-a-qfx-series-switch

Someone knows How can I do a snapshot or something similar on QFX5110? 

Many thanks !

Cheers, 
Marga : )