Clarificaiton on VLUN ID

[Murali]

Hi All,

Observed in 3PAR when a virtual volume mapped to multiple hosts the VLUN ID changes. So is it mandatory to check both the hosts use same VLUN Id ? IF same Virtual volume has multiple vlun id mapped to multiple hosts will that be causing any issue in the future please clarify.

Below is the example.

Virtual Volume --> Testlun
Mapped to host1 --> with Vlun id 1
After sometime requirement to mape the same lun to other host where vlun id 1 is already in use.

In this case is it ok to use different vlun id for host2?

Thanks,
Murali.

[Cleanur]

You should only be mapping VLUN's to multiple hosts concurrently if they are in a cluster and can handle LUN locking, otherwise you risk data corruption. Assuming you are mapping LUN's within a cluster then it would be best practice to have the same LUN Id for a given VLUN on each host. On the other hand if you un-export from host 1 and re-export to host 2, so long as they are the same O/S then the change in LUN ID shouldn't matter.

If you're not sure how this will pan out in the future then start your VLUN's at a higher LUN ID, in most cases they shouldn't need to be contiguous.

[Richard Siemers]

I think it is a ESX best practice to have all hosts see the same LUN # for the same VV (even guests too if its a RDM). Things get messy when you start to randomize those, like log files.

However, that said, I have seen Windows clusters run fine with different VLUN IDs on different nodes.

[Davidkn]

It is indeed best practice for something like VMware, but it doesn't really make any real difference these days as VMware doesn't just use the lun id, I'm not sure it even uses it at all now, it's more about disk signatures.

A storevirtual presents all luns to a host as lun 0 in VMware anyway.

It's more for identification purposes if you need to work on a particular lun, or troubleshoot etc as mentioned above.