Upgrading multiple WLC iOS, what is the correct sequence?

[CiscoBro]

We have 20 Cisco WLC 5509 that we are trying to upgrade ios.

The AP's point to 2 primary and secondary controllers.

All 300 AP's are spread out across 20 Controllers.

Question.

1. Can i upgrade firmware in controllers one by one in sequence?

2. Do i need to upgrade field recovery image version?

3. Do i need to predownload AP image before reloading WLC with new image?

4. If the latest firmware version needs a jump to an intermediate version (as per the release notes). Do i need the system to fully come up with an intermediate firmware before upgrading it to latest code. Essentially doing code upgrade twice?

Thanks in advance.

[CiscoBro]

Bump

[Leo Laohoo]

What firmware are the controllers running on and what version are you planning to upgrade to?

[CiscoBro]

Current Version--8.0.140

Trying to upgrade to Latest--8.5.140

Field recovery image version 7.0

[Leo Laohoo]

NOTE:  The latest is 8.5.151.0.

Read the Release Notes carefully.  It is not possible to go from 8.0.X.X to 8.5.X.X without upgrading to an intermediate version first like 8.2.16X.0 or 8.3.X.X. 

[CiscoBro]

Yes I am aware of that.

I am asking how should I proceed to upgrade to 8.2 version. I have 20 controllers and couple hundred AP's spread across all 20 controllers.

Do I have to upgrade primary and secondary controller that AP points to simultaneously?

[Leo Laohoo]

I'd upgrade all the secondary controllers to 8.5, move all the APs to the upgraded WLC and then upgrade the primary controllers.