Reattaching existing host to a Lun

I have two hosts (VMware ESXi 5.0) attached to a single SAN that is divided into 2 volumes.  Both hosts have connections to each volume on the SAN.  One host lost power.  Upon recovery it has lost connection to one volume.  When I do a rescan it does not see the missing volume.  When I attempt to re-add, it does not present to added to the host.  The second host has no problem.  Any help would be appreciated.
yvepaIT ManagerAsked:
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It sounds to me like an issue with Lun-masking on your san attached storage array.  I say san attached as the storage array is NOT the san, merely a node on it.  Your san consists of all san attached devices and san networking equipment - so in this case it would be your san attached storage array, your san networking equipment (fiber channel or otherwise), and the san HBAs (host bus adapters - aka the NIC for the SAN).

Anyway what your symptoms indicate (to me) is that the host that went down it lost one of its links into the san.  This could be a failure in one (of two) HBAs present in that server, or potentially even a break in a cable.  

My guess would be that the second HBA in the server that went down has not been LUN-masked to see the volume in question on the san attached array.

Lun-masking conceptually is an ACL (access control list) that limits which SAN addresses (the WWN of your fiber HBA - the WWN is analogous to MAC address in Ethernet).

My guess is that the lun mask for the volume in question only has 3 entries in its ACL
1) the first HBA of server1
2) the second HBA of server1
3) the first HBA of server2 (which failed for some reason)

You would need to add the second HBA of server2 to that ACL.  Do a rescan of devices in vcenter on server2 and you should be all set.

Good luck.

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andyalderSaggar maker's bottom knockerCommented:
How is the host attached? fibre channel or iSCSI?
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