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NickAC
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Confusion on LUN Numbering

Hi

I have a question on LUN numbering, We have Fibre Attached hosts to an EMC VNX 5500

I am looking at our existing setup and just getting a feel as i need to create some new LUNs shortly and i'm new to Fibre.

On the EMC VNX we have a LUN that has been given the LUN ID of 200, however when i match the UUID to the LUN on the host within the Fibre Card on an ESX host it shows the same LUN as LUN ID 43, i'm guessing this is OK as its been in place for a long time and working.

My question are

Why does the LUN IDs not match the IDs on the storage array

I know there is a 255 LUN ID limit in VMware, if i were to provision a LUN on the VNX side and give it a number higher than 255 would that be OK if VMware is going to give a lower LUN ID anyway.

Many Thanks

Nick

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a_p_
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A production LUN on a VNX storage system has two LUN-IDs, an internal LUN-ID as well as a Host-LUN-ID. The Host-LUN-ID is the one you can define when you present the LUN to a host, i.e. add the LUN to a storage group.

One quick hint though. I often have to deal with a large number of similarly sized LUNs and to identify them without the need to verify IDs, I usually pick a slightly different size (e.g. 1 GB). I'm doing the same for virtual disks, if a VM has multiple disks.

André

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a_p_
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A production LUN on a VNX storage system has two LUN-IDs, an internal LUN-ID as well as a Host-LUN-ID. The Host-LUN-ID is the one you can define when you present the LUN to a host, i.e. add the LUN to a storage group.

One quick hint though. I often have to deal with a large number of similarly sized LUNs and to identify them without the need to verify IDs, I usually pick a slightly different size (e.g. 1 GB). I'm doing the same for virtual disks, if a VM has multiple disks.

André

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NickAC
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Hi Andre

So when you create a new LUN and you get the option to specify the LUN ID that is the internal LUN ID and can be higher than 255

Then when you add the LUN to a storage group to present it to the hosts you get the option to specify a Host LUN ID which can be different but must not exceed 255?

Thanks for your help

Nick

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a_p_
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I don't know the LUN number maximums by heart. However, I'm not aware of a 255 ID limit. The only limit on the ESXi host that I'm aeware of, is the total number of LUNs per host, which must not exceed 256 (see http://www.vmware.com/pdf/vsphere5/r55/vsphere-55-configuration-maximums.pdf).

André

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