Change Storage Interface MTU to 9000 in Xenserver Pool

[Robert Madrian]

Hello,

 

Is it really true that changing the MTU size to 9000 on the Storage Interfaces in a Pool is only possible by deleting and reconfiguring the Interfaces?

(in Xencenter this option is deaktivated)

 

we have two pools with 17 Servers (Xenserver 6.2) and many Interfaces in an running environment and I don't want to change this with deleting the Interfaces...

 

robert

[Konrad Ruess]

I've done this with a CLI command, no need to recreate the network:

 

1) shut down guests

2) reconfigure the network

# xe network-param-set uuid=<network-uuid> MTU=9000

3) reboot hosts

4) verify proper MTU sizing

# ping -M do -s 8972 -c 2 <ipaddr-of-storage>

 

Instead of rebooting the hosts, I've also seen reports that unplugging / plugging the PIF's would do the trick, but I didn't check that by myself.

 

BfN, Konrad

[Tobias Kreidl]

I don't believe they need to be destroyed -- you may need to put the server into maintenance mode, though, depending on which interfaces are involved. See also: http://discussions.citrix.com/topic/365124-change-mtu-of-storage-interface-on-a-pool/

[Robert Madrian]

does it mean that if I bring the pool in maintenance mode that I can change the MTU in our Storage Interfaces (two NICs) - this is not the Managment Interface?

 

robert

[Robert Madrian]

I have tested this on a testserver but cannot change MTU on Storage Interface also in maintenance mode (see picture)

 

[Tobias Kreidl]

Hmm... let me investigate later on when I get a chance. Did you try the CLI option?  Meanwhile, please see: http://discussions.citrix.com/topic/300432-adjust-the-mtu-of-the-primary-management-interface-in-xenserver-6/

 

-=Tobias

[Robert Madrian]

Hi Tobias,

 

do you had the time to look into it?

 

robert

[Tobias Kreidl]

Some. I did not find a definitive answer, other than it appears in any case that a reboot is necessary. Sorry, I had a major meeting overload today!

[Alan Lantz]

Jumbo's may not give you enough return on your hours invested. 

 

--Alan--

[Tobias Kreidl]

It's typically around 10-15% gain fpr jumbo frames.  You'd be best off to either create a new PMI and migrate it all over to it and rebuild the bond, or to be safest, take everything down and reconfigure it.  I recall trying to do something like this on the fly once with a much older version of XenServer (6.1, perhaps) and it was not a happy ending.

[Robert Madrian]

this is weird that such a trivial Setting can only applied with rebuilding the interfaces!?!

 

robert

[Alan Lantz]

Not really rebuilding, but the interface can't be in use. If you have additional physical interfaces you could setup new storage with the larger MTU and do a migration. Or if what you have is in use you would need to shut down all of the VM's so you could then change the MTU. 

 

--Alan--

[Tobias Kreidl]

Being totally shut down is the key here, unless you can create and swap on the fly, which I think is possible, but fraught with peril! If it were that easy to do, there'd be solid documentation on how to do an on-the-fly change.

 

-=Tobias

[Robert Madrian]

Hi, do you mean I have to restart the Host and then I can Change the MTU in Xencenter?

 

on my testserver there is no VM and I changed to maintanance mode but still the MTU Setting is grayed out/Disabled...

[Tobias Kreidl]

I think the only way to do this is to probably destroy and re-create the network.

[Alan Lantz]

I could have swore I don't that by just shutting down VM's, but honestly its been so long ago I could be mistaken. And if you have to shut everything down deleting/adding an interface doesn't really add much time to the process. 

 

--Alan--

[Tobias Kreidl]

I tried bringing a server all the way down to maintenance mode (obviously, with no VMs running) and even then could not change the MTU.

[Alan Lantz]

Well thats a bummer because I thought you could. But at that point deleting and recreating an interface isn't a big deal. Very odd with it not in use we can't change the MTU. 

 

--Alan--

[Tobias Kreidl]

If the storage is not active, it may be possible to do this pool-wide with the xe "network-param-set" command (thanks, Jesse, for the tip!) but I'm not sure if (1) that will work with an active storage network or, (2) if it can be done if the NIC is part of a bond. If it's on a VLAN and the MTU of the NIC or bond itself would be exceeded, that certain;y won't work. You may have to do some additional experimenting on a test setup.

 

-=Tobias

[Robert Madrian]

That worked perfect - thank's

 

robert

[Tobias Kreidl]

Yes, network-parm-set is indeed the secret! Thanks for confirming that, Konrad!

[Konrad Ruess]

Welcome - I'll do what I can... ;-)

 

Und Tschüss,

Konrad

[David Ross1709151782]

On 2/22/2017 at 10:13 PM, Konrad Ruess said:

I've done this with a CLI command, no need to recreate the network:

 

1) shut down guests

2) reconfigure the network

# xe network-param-set uuid=<network-uuid> MTU=9000

3) reboot hosts

4) verify proper MTU sizing

# ping -M do -s 8972 -c 2 <ipaddr-of-storage>

 

Instead of rebooting the hosts, I've also seen reports that unplugging / plugging the PIF's would do the trick, but I didn't check that by myself.

 

BfN, Konrad

 Toolstack restart has worked for me. No need to reboot. However I'm using XenServer 8.1