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switch switches between SAN and ESX 4 host server

Posted on 2010-09-07
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Last Modified: 2012-05-10
Greetings,

I am hoping this is as easy as I imagine. I have (2) switches. One connects my (2) ESX 4 hosts to my EMC AX4-5i, the other is in the rack connected to nothing. Can I give the unconnected switch the same IP as the connected one, unplug all cables from the connected one and plug them into the unconnected one, and then be connected to the SAN with no further configuration on either the SAN or the ESX 4 hosts? I have enabled jumbo frames on the unconnected switch to match the connected one - that is the only thing I can think of that would need to be configured as I did nothing else to the connected switch (no VLAN, no QOS, etc.).

Please feel free to ask for clarification.

Thanks a lot.
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Question by:rpliner
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22 Comments
 
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Assisted Solution

by:jorlando66
jorlando66 earned 200 total points
ID: 33619678
If the two switch configs are the same as you say then yes you can connect as you describe.  The new switch will take over the role of the old switch.
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by:Gianpiero Rossi
Gianpiero Rossi earned 200 total points
ID: 33619736
If jumbo frames are already enabled on esx and old switch, i guess all should be running.

Can i suggest to you something?

to have a better HA, you can both switch between the esx and the Sans. To think at the best topology i would liek to knoe how many nic do you have in the esx for the vmk ports


Jumpa
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by:rpliner
ID: 33619861
jorlando66 - the configs are the same.

gpiero74 - I have 2 switches on different subnets running from the esx hosts to the SAN. I have 4 NICs for the SAN (2 on the .50 subnet and 2 on .100 subnet) on each host.

As it seems possible to unplug/plug between the switches, my next concern is how that will affect my servers running from the SAN. if I unplug/plug I am concerned about data loss, especially on my exchange server and file server so I guess I may have to come in very early one day to switch the cables.

Thank you both for your input and quick responses.
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LVL 28

Expert Comment

by:bgoering
ID: 33620154
If you have iSCSI multipathing configured and working you should be able to move one link at a time. If you don't it would be better to find a time when you can take things down to make the change.

Good Luck
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by:rpliner
ID: 33620192
bgoering - I am using the MS iSCSI initiator and MPIO as well as powerpath (EMC software). However, my concern is having both switches running and connected while having the same IP address. Should that be a concern? If not, I am considering pulling one and seeing what happens. Thanks
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by:bgoering
ID: 33620256
Why do the switches need the same IP address? Isn't it only used for switch management? I wouldn't expect there to be any issue with the management IP address of the switch as your iSCSI traffic doesn't need to talk to that IP address anyway.

If it is of concern couldn't you give the new switch a different IP address while cutting over, then when you retire the original switch you could change the IP address on the new switch back to the original.
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Author Comment

by:rpliner
ID: 33620420
bgoering - the SAN requires each of the 4 iSCSI ports to list a default gateway (this should be the IP of the switch between the SAN and the ESX host, according to the manual). So if I use a different IP, I'll have to change that on the SAN. I was looking for a way to do it without reconfiguring anything on the SAN and/or ESX hosts and/or Windows Server VMs and without having to come in early or shut down any servers.
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Expert Comment

by:bgoering
ID: 33620693
Is your SAN storage on the same IP subnet as the servers? Or is routing and a gateway required to reach the storage. I know that for software iSCSI with vSphere ESX or ESXi the VMkernel port must be in the same subnet as the storage. In other words no routing to storage is allowed. This restriction may not hold for independent iSCSI HBA's installed in the host. I don't believe that restriction holds for the MS iSCSI initiator you mentioned.

In any event, if the SAN is on the same subnet as the Initiator the gateway won't be used, and you should still be OK even if it temporarily has a different IP address.

Are you using the iSCSI SAN to present LUNs used for VMFS Datastores?

Documentation: from iSCSI SAN Configuration Guide for vSphere 4.1:

"CAUTION If the NIC you use with your iSCSI adapter, either software or dependent hardware, is not in
the same subnet as your iSCSI target, your host is not able to establish sessions from this network adapter to the target"
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by:rpliner
ID: 33620994
bgoering - the SAN is on the same subnet. VMkernel is on same subnet as well. I am using the iSCSI SAN to present LUNs. I originally gave the unconnected switch the IP of 192.168.100.2 (the connected switch is 192.168.100.1), connected it to an open NIC port on one of the ESX hosts, created a vSwitch, configured an adapter in a windows VM to that subnet, then assigned it to the newly created vSwitch. However, I am unable to ping the 100.2 switch from that windows VM. Can ping 100.1 switch (it has been in production for about 5 months now).
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Expert Comment

by:bgoering
ID: 33621109
I know you said that you haven't configured any VLANs, but if the switch is VLAN capable (sounds like it probably is because you can give it an IP) it will have a default VLAN. Typically (at least on Cisco equipment) that is VLAN 1. For things to work properly you will need to, at least temporarily, link the two switches together.

What kind of switches are you using?
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by:rpliner
ID: 33621300
the connected switch is a Cisco Small Business (remarketed Linksys) SLM 2024. The unconnected switch is an HP 2910al. I don't see why I can't ping the HP though. It has an IP on the same subnet as the adapter in the windows VM (.100) and the physical cable is connected to the host server and the switch. I can ping everything else on the .100 subnet (connected switch, VMkernel port IP, and the SAN ports). vCenter shows that the windows VM is on the newly created switch on the network config page.
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bgoering earned 1600 total points
ID: 33621427
Try patching the two switches together - If there is an uplink port on one of the switches use that to connect to any port on the other. If there isn't a crossover cable would be best, but possibly not necessary as many of the Linksys (Cisco) switches support sensing to determine what mode the port needs to be in.

See if ping works that way. I wouldn't expect ping to work even with a new VMkernel port and nic connected to the second switch unless you were to use an entirely seperate subnet for the 2nd switch because the ping is only going to take one physical path. So unless the switches are linked one will always work and the other always won't.

If you want to test before linking your switches together set your second switch to 192.168.200.1/24 and your VMkernel port to 192.168.200.x/24 (leave default gateway alone) and see if you can ping 192.168.200.1 from your ESX host. That will verify at least the cabling.

Again, so long as the SAN and iSCSI initiators are on the same subnet, the management address as the default gateway won't make any difference (and could actually be any address). At this point it is simply a layer 2 switch and will connect any two hosts on the same IP subnet.
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Author Comment

by:rpliner
ID: 33621431
I just noticed in vCenter that my newly created vSwitch does not have an IP range assigned as the rest do. The network adapters observed IP range shows none. How do I configure that? I don't remember manually adding that for the other vSwitches and I have 2 for the SAN subnets and 2 for the LAN and they all show the correct observed IP ranges in vCenter.
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Expert Comment

by:bgoering
ID: 33621516
You have to create a VMkernel port group on the new switch in order to assign an IP address. No observed ranges are showing because there is no traffic on the new switch yet.
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LVL 7

Author Comment

by:rpliner
ID: 33621549
I did create a VMkernel and gave it a .100 IP (192.168.100.7). I then added a virtual machine group and added the windows VM I have been testing with. Still can't ping. Observed IP still shows none. Thanks for your help with this.
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Expert Comment

by:bgoering
ID: 33622574
Did you ever link your switches together?
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by:rpliner
ID: 33622677
bgoering - had to leave the office for a meeting. I will do what I can remotely but will definitely link the 2 switches in the morning when i get in. Will that allow me to, eventually, remove the cisco and use only the HP? Thanks again for your help.
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LVL 28

Expert Comment

by:bgoering
ID: 33623136
OK, I am home for the day also but will look in tomorrow. Linking the switches shouldn't impact your plans. Once everything is moved over just unlink them then change the IP address on the HP to what you want going forward.
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by:rpliner
ID: 33627457
bgoering - linking worked. I am able to ping the HP switch. So now what exactly? Thanks again.
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Assisted Solution

by:bgoering
bgoering earned 1600 total points
ID: 33627782
Well now what. So long as you are certain multipathing is working properly you should be able to patch over one uplink at a time. To be safe I would probably wait until after hours or a slow time, but multipathing should fail over any I/O to the remaining path.

Then you can remove the link, change the IP address on your new switch, and retire your old switch.

Good Luck
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Author Comment

by:rpliner
ID: 33627805
bgoering - excellent. Thanks again for your help.
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Author Closing Comment

by:rpliner
ID: 33647922
It would likely have worked to just pull the cables and plug them into the new switch but linking the switches ensured I wouldn't lose connectivity as I have multipathing correctly configured. Worked easily one at a time. Watched links go from active to inactive to active in about 10  - 15 seconds.  
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