ESX and continuous access

inex — Wed, 04 Aug 2010 19:47:22 GMT

Hi

When using continuous access between 2 EVA's + vsphere (no srm) and when ESX server is shut down and luns are failed over to the secondary EVA, the same server is booted up with access to luns on secondary EVA, is it then necessary to do a add storage on the ESX server to see the luns again?

-inex

Re: ESX and continuous access

Uwe Zessin — Thu, 05 Aug 2010 06:59:25 GMT

It is not possible to give a simple yes/no answer, because there are several factors which can make it necessary to do a force-mount or resignature.

Can you test it with a separate single virtual disk?

Re: ESX and continuous access

inex — Thu, 05 Aug 2010 20:29:00 GMT

yes, we will test this, but I do know what kind of factors you are thinking of here

Re: ESX and continuous access

Uwe Zessin — Fri, 06 Aug 2010 06:21:56 GMT

I have not seen a detailled description of all the factors ESX uses to try telling the difference between the original volume and a snapshot/clone/replication in once single place and when a specific item is applied - maybe it does not even exist.

A commonly known item is the LUN address (sometimes called the "LUN ID" or "LUN Number"/"LUN #").

Another one is the "SCSI inquire string". I don't know if it is still used in current ESX 4.x, but in previous versions it was used, too. This was noticed when one did replicate between different EVA controller models, e.g. EVA8000 (HSV210) and EVA4000/6000 (HSV200).

And then there is the "LUN WWN" (a 128-bit value starting with "6" and provided in a SCSI page), which in most cases is identical to the virtual disk's internal UUID. It is sometimes called the "LUN ID" or "LUN serial number".
If the old one gets lost due to a snapclone, mirror clone or maybe after a CA failover, you can modify the virtual disks's "LUN WWN" back as long as the vdisk is not presented. But make sure no other vdisk uses the same value.

I've put together some VMware Knowledge Base articles you might find interesting to read.

1005751 - Resignaturing VMFS3 volumes from the command line
http://kb.vmware.com/kb/1005751

1011387 - ESX/ESXi 4.x handling of LUNs detected as snapshot
http://kb.vmware.com/kb/1011387

1015986 - Force mounting a VMFS datastore residing on a snapshot LUN results in the error: Cannot change the host configuration
http://kb.vmware.com/kb/1015986

1017469 - Missing LUNS after upgrading to ESX/ESXi 3.5 Update 5 or ESX/ESXi 4.x
http://kb.vmware.com/kb/1017469

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