(image care of www.interestingfacts.org)
If you have Brocade fibre channel switches in your SAN, you need to be aware of the method which Brocade use to manage firmware releases. All 4 and 8 Gbps Brocade SAN switches use a Linux based firmware which Brocade call Fabric Operating System or FOS. Updates to this firmware are released in families. This started with version 4, then version 5 and then version 6. Each family has had a series of updates. Version 5.0.x went to 5.1.x, 5.2.x and 5.3.x. Version 6.0.x went to 6.1.x, 6.2.x, 6.3.x and currently 6.4.x.
The good news is that you can non-disruptively update firmware on Brocade switches:
So you can move to higher releases without an outage (note there may be exceptions to this, always read your release notes to be sure).
However you need to be aware of a rule regarding the from and to versions. Since FOS 6.0.0 Brocade have a one-release migration policy. This allows more reliable and robust migrations for customers. By having fewer major changes in internal databases, configurations, and subsystems, the system is able to perform the upgrade more efficiently, taking less time and ensuring a truly seamless and non-disruptive process for the fabric. The one-release migration policy also reduces the large number of upgrade/downgrade permutations that must be tested, allowing Brocade to spend more effort ensuring the supported migration paths are thoroughly and completely verified.
Disruptive upgrades are allowed, but only for a two-level migration (for instance from 6.2 to 6.4, skipping 6.3).
So why should you care?
Well your upgrade philosophy may be: If it aint broke, don't fix it. Or you may have the policy: We do fix on fail, apart from that, we don't update firmware. Much as I can understand the attraction of this, when you finally do perform an update, you may find yourself having to do many upgrades or kangaroo hops as I call them.
Lets document some possible kangaroo hops from an old to what is currently the newest release:
4.1.2f → 4.4.0e → 5.1.1b → 5.3.2c → 6.0.1a → 6.1.2c → 6.2.2b → 6.3.1a → 6.4.1b
As you can see from the steps above, you may have a very long change window if you are choosing to not perform updates on a regular basis. There are also lots of caveats and restrictions based on the hardware of the switch you are running. It is very important you consult the release notes that can be found at the following links:
IBM SAN b-type Firmware Version 4.x Release Notes
IBM SAN b-type Firmware Version 5.x Release Notes
IBM SAN b-type Firmware Version 6.x Release Notes
If your looking for a recommended version to install, the Version 6 release notes page above gives advice on this. Currently it says: IBM recommends that Open System customers that currently use FOS 6.1 or earlier limit migration to FOS 6.2.2b, 6.3.0d, 6.3.1a, or 6.4.0c or later only.
Please notes that the release notes published on IBM's website are Brocade documents. While this is good (since it means they come straight from the manufacturer), you need to decode which Brocade hardware model is which IBM machine type. The version 6 URL above also contains a product cross-reference which lets you convert Brocade product names to IBM product names. I am also working on a post which will help you with this, so watch this space.
Edit July 19, 2011. The original post suggests 6.4.0a as a go-to level, this has since been removed. It has also been pointed out to me that some blade type switches may not be capable of hot-code-load (HCL). You need to check your vendor release notes to be certain.