@AjitKumar is correct. You cannot currently step the upgrades. Is there any particular reason why you'd want to do this? If it is for stability testing do you have any other networks with fewer APs? We typically do firmware updates on those smaller networks first to make sure things are stable before rolling it out to our sites with more APs. One potential, but not ideal, option would be to split your devices into two networks. But that would be only if you absolutely have to do them separate and have no other networks.
I would like to see the APs to more gracefully update their firmware on the same network so that there is virtually no outage. An AP should stop accepting clients, handoff its current clients to a nearby AP, and then update its firmware. Once the update has been verified, then it can make itself available for clients and then the next AP will update until all APs are updated.
Are you in a 24x7 environment where you can't schedule evening maintenance windows?
Not 24x7 but I have some devices that do not reconnect properly when the wifi network completely disappears. We have to restart them whenever we do a firmware upgrade.
Thanks for replying!
I'm sure that it's difficult to update MRs partly...
Could someone know all MRs update at a time, or different timing?
Similar devices in a single network update at the same time.
Also I believe the firmware size is in MBs.
However I shall reiterate the upgrade download is negligible. I have not experienced heavy downloads atleast for MRs.