Force10 Operating System 9.10 changes maximum MTU size

Force10 operating system (aka FTOS, DNOS) always had the maximal configurable MTU size per port 12000 bytes. I have just been informed by former colleague of mine that it is not the case since FTOS 9.10 and above. Since FTOS 9.10 the maximum MTU size per switch port is 9216. If you used MTU 12000 then after upgrade to firmware 9.10 the MTU should be adjusted automatically. But I have been told that it is automatically adjusted to standard MTU 1500 therefore if you use Jumbo Frames (9000 bytes payload) it is necessary to change configuration before upgrade from 12000 to 9216.

Disclaimer: I had no chance to test it so I don't guarantee all information on this post are correct. 

UPDATE: Please read comments below this article for further information and great Martin's explanation of real MTU behavior. Thanks Martin and Kaloyan for your comments.

Martin's comment:

MTU 12000 in configuration was not reflecting real hardware MTU of underlaying chipset, after upgrade to 9.10 it's just adjusted to reflect real hardware MTU. Tested on S4048 9.10(0.1). When you boot into 9.10 you can see log messages saying that configuration is adjusted to reflect real maximum hardware MTU.
Also in configuration

 ethswitch1(conf-if-te-1/47)#mtu ?  
 <594-12000> Interface MTU (default = 1554, hardware supported maximum = 9216)  
 ethswitch1(conf-if-te-1/47)#mtu   

                                 

Excellent article: "Anatomy of an Ethernet Frame"

Trey Layton (aka EthernetStorageGuy) wrote excellent article about MTU sizes and Jumbo Frame settings. The article is here. In the article you will learn what MTU size parameters you have to configure in the path among server, network gear and storage. It is crucial to understand difference between payload (usually 1500 or 9000) and different frame sizes (usually 1522 or 9018 or 9022 or  9216) on networking equipment.

Here is summation of  Trey's deep Ethernet frame anatomy in to the simple best practice. "If you want to implement Jumbo Frames use pure datacenter networking equipment and setup MTU size to the device maximum which is usually 9216."