Azure Hybrid & Cloud Migration Blog

Author: Zahir Hussain Shah, MVP Exchange Server

Interesting Storage Power-Path software upgrade on Hyper-V Servers, where you are using SAN LUNs for VHDs and Pass-Through Disk for VMs internal storage.

Categories: EMC Power-path | Microsoft Exchange Server 2010 | Hyper-V Pass-Through Disks | Hyper-V

Introduction to Hyper -V Pass-through Disks:
Within Hyper-V, Microsoft introduced a method of taking the physical disk, mounted on Hypervisor to be taken inside the Virtual Machine (VM), which provides a nifty way for the Administrator, those who dose not want to create the second VHD for the D:\ (additional drive / application partition) inside the VM, for taking the Physically mapped SAN LUN or Physical Server disk as pass-through and taking inside the VM, you have to make the disk offline, and then you will go to Hyper-V for the particular VM, and needs to add SCSI Controller, and then ADD DISK, and from down, you will add the offline disk on the computer, with the DISK name, e.g. DISK 5.

Problem: How upgrading EMC Power-path will make issue for me?

Recently, while upgrading my companys SAN from EMC Clarion to EMC VNX, we had to upgrade the firmware and power-path version to the newest one, so what we did, we mistakenly first removed the power-path old version, which was earlier recommended by the Vendor, so when we removed it and then reinstalled, so all the drives came back only (physically mapped to Hyper-V Server), since they were offline when the came back after installing power-path, so we thought it is fine, because we want the m to stay as offline, as they have been taken inside the VM as pass-through disk, but when we tried to start the Exchange Server 2010 Mailbox Server, so it gave error that Microsoft SCSI Controller ID is different and Microsoft Hyper-V doesnt have permission on this GUID / UIIIDs (SID) of disk.

Solution:

So then we had to remove all the disk (pass-through), and start the VM, so we found that the VM came online successfully, then we added all the disk in the same original order, which we removed earlier, and then start the Server so this time Server came online with all the necessary drives, along with same Drive letters, which helped to continue Exchange Replication Services.

What if I dont remove the EMC Power-path and perform the in-place upgrade the EMC Power-Path?

After the removal of EMC Power-path, we also tried to perform the in-place upgrade of power-path newer version, and it went fine, but when we restarted the Server (Hyper-V), so we found the disk offline, and hit the VM start, but the we found the sam e error that the SID (UIID / GUID) has been changed or the Hyper-V doesnt have permission on this GUID.

Observations:
It seems that when we perform the power-path upgrade, whether by removing the old version first or perform in-place upgrade, it changes the GUID / UUID of the SCSI Con troller ID for the Disk, so when the Hyper-V searches for the same UIDs or GUIDs, which turn Hyper-V fail to start VM.

After upgrading Power-path, suddenly the Virtual Machine gets disappeared :$
During the same maintenance activity, I found that one of my critical machine got disappeared from the Hyper-V, I was so much shocked to see that, what exactly happened, whether I mistakenly removed it or something else happened?, but after that when I mounted and dismounted the Physical Disk where I was having the VHD created for the VM, and then Hyper-V sensed the presence of the VHD, and refreshed the Hyper-V Management Console, so I found that Virtual Machine came back, but UNFORTUNATELY, one of my VM got completed disappeared, and to somehow VM and its corresponding Virtual Machine Configuration files got deleted.

Best Practice, which I observed during this whole maintenance activities, shutting downing Hyper-V VM will not help in anyway, you have to Stop and Disable the Hyper-V related services on the Server, and only after that if you perform the Power-Path upgrade, so maybe, you will to pinch your hairs little less.

I hope with this information presented in this article, you will go through less pain, and will make your transition more smooth and seamless for your virtual environment.

Note:
It may be expected that the findings, which I presented here, could vary from your environment and experience.

Cheers!