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Fault domain MTU question
Hi I would like to know is it possible to have a Physical Fault domain with a different MTU as a Virtual Fault domain that shares the same ports. According to what I see in DSM config options it "seems" possible. But would like to know if anyone has done this. The reason is that I need a different MTU for replication to a DR site, but do not have any additional free physical NICs to create a new dedicated physical fault domain.
Currently I have two physical fault domains with 4 ports each.
So the plan is to "steal" all physical ports from one of the current fault domains, and create two new fault domains from them: one virtual, one physical, each using the same physical ports (but different vlan tag for each fault domain, and different MTU - one standard frames, one jumbo). The physical one would be for the new replication traffic (MTU 1500) and the virtual one would be used as a standard front-end I/O fault domain (MTU 9000)
I asked copilot a while back and presented my plan to them; they basically said "it should be possible", but that's not overly convincing. A little disappointing to be honest from supposedly the best support around.
Thanks all
dell-richard g
605 Posts
1
October 2nd, 2017 14:00
Hi Bryan
Yes, both the physical and virtual FD MTUs are separate from each other. I can change one FD MTU and it will not affect the other. I changed the physical MTU and it did not modify the virtual. I also changed the virtual FD MTU and it did not change the physical FD MTU.
So, from a GUI standpoint, you can do what you originally asked.
dell-richard g
605 Posts
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September 29th, 2017 01:00
1, What SC platform/model are you using? (i.e. SC2000?)
2. What SCOS and DSM version is installed?
3. This is not a typical network configuration one would setup with SC, hence the silence in responses.
When ports are assigned to a fault domain (FD), the MTU is set at the FD level and that gets propagated to the physical ports assigned to that FD. Also, when a port is assigned to a FD, it can't be shared with another FD. (Maybe earlier SCOS versions with certain SC platforms may have allowed it).
I can try to look a little further on this if you answer the above questions.
bealdrid2
117 Posts
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September 29th, 2017 05:00
Hi Richard. Thanks for the reply.
1. SC9000
2. DSM 2016 R3.11 (build 16.3.11.2)
3. You're right. But Compellent sold us on the flexibility. Currently our environment can't support the typical two FD/two subnet model with one overall MTU. Your comment that
Seems at odds with the documentation in the DSM administrators guide. Please see the concept of "Virtual Fault Domains" and VLAN tagging. That is what I'm trying to do here.
bealdrid2
117 Posts
0
September 29th, 2017 18:00
Hi Richard. Thanks again.
SCOS version is 7.1.4.4. We are looking to update to 7.1.20 during our maintenance next week.
So actually I do not see a "MTU" option when creating a physical fault domain either. The MTU option only seems available if you "Edit Settings" for a fault domain. So my question is, if we create a "Virtual Fault Domain", can we then go in and edit it, and set the MTU? Do you have a test system to check to see if, for a virtual fault domain, you can modify the MTU after the virtual fault domain is created, via the "Edit Settings"? This would help me a lot to find out.
-Bryan
dell-richard g
605 Posts
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September 29th, 2017 18:00
Hello
Apologies for the delay
When you said that you had four ports per physical FD, I was thinking that you had the SC2000 which has four ports per controller. This platform does not support multi-vlan tagging (and sharing of ports between physical and virtual fault domains).
But since you have the SC9000, this will have the T5 NIC which supports multi-vlan tagging that you ask about. I looked at the T5 settings under a virtual FD (via create vlan copy), but there is no option to set the MTU on the virtual FD. The only place to set the MTU is at top level FD.
In your original post, you mentioned that with DSM, it "seems" possible, but I did not see a MTU option to set a MTU when creating a virtual FD. Is your issue that you see MTU listed and does not work, or are you saying that the MTU option is not available to be set under the virtual FD.
Also, what SCOS version are you running?
dell-richard g
605 Posts
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September 29th, 2017 18:00
Bryan
I had a SC3K and T520 NIC and I created a virtual FD and did not see a MTU setting during the creation. I did not go back and try to "edit" the virtual FD settings to see if a MTU was available, but will do so by Monday. Also, in the DSM user's guide, it listed all settings available during the creation, but does not list MTU as an option. Will get back to you by Monday.
dell-richard g
605 Posts
0
October 2nd, 2017 12:00
Hi Bryan
I was able to get on a system (SC9000) that had DSM 16.3.11.2 and SCOS v7.2.x and yes, there is a MTU selection option when you do an EDIT on the vlan copy fault domain.
Looking at the physical and virtual FD MTU settings, they appear to be separate. The physical FD is currently set at 9K, and the vlan copy default MTU came up as 1500, and the selection allowed different MTU settings. Attached is a screen shot of the virtual FD settings that shows a MTU selection.
Does this answer your question?
bealdrid2
117 Posts
0
October 2nd, 2017 13:00
Hi Richard
Yes, thanks it does. It seems like what I'm after is possible; at least in the GUI. I don't know if it'd be possible for you to reverse the setup, and have the physical fault domain set at 1500MTU and the virtual one at 9000. If you can try that I'd appreciate it, since that will mirror my config.
Thanks again,
Bryan
bealdrid2
117 Posts
1
October 2nd, 2017 15:00
Richard I greatly appreciate your efforts here. I will be proceeding with our maintenance and will update this thread with how it goes.
--Bryan