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 Post subject: Adding an RDM LUN
PostPosted: Tue Nov 13, 2018 1:42 am 

Joined: Mon Jul 03, 2017 9:05 pm
Posts: 12
Hi Team,

Our ESXi team is trying to add an RDM LUN to a VM cluster and receiving error like "Incompatible device backing specified for device ‘0’"

As per the update from them, the replicated LUN which is part of 2 different data centers should be having identical LUN ID to add the RDM LUN to the metro cluster. What I thought was LUN ID doesn't matter and only naa id matters for any configuration as it is only considered for allocation. Here naa id is identical for both arrays in different location. But the LUN ID is different.

LUN ID 59 on target has already been occupied by other VV due to which other LUN ID 81 has been assigned as ID 59 was not available. This is assigned automatically as part of VVSet creation.

How can we change the LUN ID on both side as either 59 or 81 or any new one so that the LUN ID also will be identical.

Is there any option to perform this without unexporting the LUN's and then exporting again with required changes. We can't have downtime for the LUN. We are ok with if a new LUN ID other than 59 or 81 can be assigned to both array as well online too. Any help will be appreciated

3PAR version 3.2.2 EMU4

Thanks in advance.


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 Post subject: Re: Adding an RDM LUN
PostPosted: Tue Nov 13, 2018 5:14 am 

Joined: Wed Nov 09, 2011 12:01 pm
Posts: 298
I believe there is a setting within VMware that allows for mismatch in LUN IDs not sure if it'll help with RDM, depends if presented to the ESXi host or direct to the guest.

We first setup peer persistence when we replaced one of our main arrays so had the chance to start all source LUN IDs from 100+ on the new array and hence allowing us to match IDs for hosts.

If the blocking VV is VMFS you could Vmotion the data off it and remove it to free the LUN ID but you are bound to hit the same issue again.

I've also had to stop using VVsets to export groups of LUNs as they can be unpridicable with LUN IDs and make it difficult to match, I now export each VV individualy so I can make sure IDs match.


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 Post subject: Re: Adding an RDM LUN
PostPosted: Tue Nov 13, 2018 5:48 pm 
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Joined: Tue Oct 07, 2014 8:34 am
Posts: 172
https://community.hpe.com/t5/3PAR-Store ... 5015#M4675


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 Post subject: Re: Adding an RDM LUN
PostPosted: Tue Nov 13, 2018 5:51 pm 

Joined: Mon Jul 03, 2017 9:05 pm
Posts: 12
ailean wrote:
I believe there is a setting within VMware that allows for mismatch in LUN IDs not sure if it'll help with RDM, depends if presented to the ESXi host or direct to the guest.

We first setup peer persistence when we replaced one of our main arrays so had the chance to start all source LUN IDs from 100+ on the new array and hence allowing us to match IDs for hosts.

If the blocking VV is VMFS you could Vmotion the data off it and remove it to free the LUN ID but you are bound to hit the same issue again.

I've also had to stop using VVsets to export groups of LUNs as they can be unpridicable with LUN IDs and make it difficult to match, I now export each VV individualy so I can make sure IDs match.


Thank you for the update.. Manually exporting was not done as the no: of VV's to be exported is nearly 100. So it is not an easy task to individually add one by one. I will check with ESXi team whether any settings are available from VMWare itself.

Thank you again for the reply


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 Post subject: Re: Adding an RDM LUN
PostPosted: Wed Nov 14, 2018 5:47 am 
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Joined: Tue Oct 07, 2014 8:34 am
Posts: 172
You should clean up this on Storage side.
I have done this for a Customer with 180 VV, need 6h.


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 Post subject: Re: Adding an RDM LUN
PostPosted: Wed Nov 14, 2018 6:47 am 

Joined: Mon Jul 03, 2017 9:05 pm
Posts: 12
cali wrote:
You should clean up this on Storage side.
I have done this for a Customer with 180 VV, need 6h.


Oh, you added 180 VV manually. But what I thought was LUN ID doesn't matter what ever it may be as naa.id only considered. But now I heard from VM team that they attached the RDM disk after rescanning. Not sure how it worked after re-scanning it. Need to get more details from them. I didn't made any changes from Storage side.

Initially what VM team has provided us was below doc vm kb article which says same LUN ID is required for resolving this issue

https://kb.vmware.com/s/article/2054897


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 Post subject: Re: Adding an RDM LUN
PostPosted: Wed Nov 14, 2018 8:14 am 

Joined: Wed Nov 09, 2011 12:01 pm
Posts: 298
Same LUN ID is preferred by a lot of OSes so it's good practice to do that, not all can be worked around.

Matching WWNs is the minimum for ALUA to work, beyond that are the TPGID values that are used to tell the primary and secondary volumes apart those values change when you take a normal LUN and turn it into a Peer Persistence/ALUA LUN, a rescan or sometimes reboot is required depending on the OS to notice the change.


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 Post subject: Re: Adding an RDM LUN
PostPosted: Mon Dec 03, 2018 1:17 am 

Joined: Mon Jul 03, 2017 9:05 pm
Posts: 12
ailean wrote:
Same LUN ID is preferred by a lot of OSes so it's good practice to do that, not all can be worked around.

Matching WWNs is the minimum for ALUA to work, beyond that are the TPGID values that are used to tell the primary and secondary volumes apart those values change when you take a normal LUN and turn it into a Peer Persistence/ALUA LUN, a rescan or sometimes reboot is required depending on the OS to notice the change.


Without changing the LUN ID, ESXi team managed to do it.. Will check with them and update how they did it.

Thank you all for your help...


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