Recommendation would be to use 8080f (non-ufi) as an intermediate code. Your upgrade path would look like this:
8070d > 8080f (non-ufi - same format as 8070d) > 8090d UFI (new file format - everything in one file)
Obviously not having console access is a downside should anything arise during the upgrade. That would really be your call on how critical the stack is to your business. I would not expect to have any issues, but you never know. If you would like assistance with the upgrade, I would recommend opening a support case.
Ben Beck, RCNA, Principal Technical Support Engineer support.ruckuswireless.com/contact-us
To be sure, do you think that from the satck IP management, if I download the code using tftp server on site, the code will be copied automatically to all the stack members and then all the stack members will be upgraded at the same time?
This is my question before proceding with the upgrade job