Hi,
I'm right now testing a couple of QFX5200 in the lab to put them into production later as a L2/L3 device. Regarding the datasheet, the device actually does support (T)ISSU for seamless upgrades: http://www.juniper.net/assets/de/de/local/pdf/datasheets/1000560-en.pdf
"• Topology-Independent In-Service Software Upgrade (TISSU): On the QFX5200, two instances of Junos OS VMs run in a Linux-based virtualized environment, one in active mode and the other in standby mode. During a software upgrade, the switch seamlessly moves from the active Junos VM running the current software version to the second standby VM running the newer version while maintaining intact data plane traffic. This true topology-independent ISSU—an industry-first for a fixed-configuration, single CPU top-of-rack switch—is supported across all Layer 2 and Layer 3 protocols, and does not req"
However, this page says something else: http://www.juniper.net/documentation/en_US/junos15.1/topics/reference/requirements/issu-system-requirements-qfx5100.html
"Note: The QFX5200 switches do not support ISSU."
Since there is only one JunOS available right now, I simply installed the same JunOS on the device that was already running there. Since there is no in-service-software-upgrade command, I used the regular one assuming, that the VM switchover would now be done automatically without further intervention required be me. But actually that wasn't the case and even if the Host OS was completely identical, the system said, that a Host OS upgrade will be forced as well. The upgrade itself took about 10 minutes and the device was completely offline meanwhile. The question therefore is: which information is correct? Does the device support ISSU or not? If not, will it support it in the future? Thanks for any suggestions.