While I was poking around in my Twitter timeline, a tweet from Victor van den Berg (VCDX #121) got my attention.
@Mandivs I'm suprised W2K12R2 MSCS doesn't support in guest iSCSI anymore…You have to use vSphere 5.5 RDM's
— Viktor van den Berg (@viktoriousss) February 11, 2014
My first though “What a step backwards!”. I have installed a bunch of Microsoft clusters in Virtual Infrastructure and vSphere enviroments and most times it was PITA. Especially with Raw Device Mappings (RDM) and bus sharing, which prevents vMotion a VM to another host (regardless of this: it’s not supported!). It’s ironic to invest a significant amount of money into a technology, which increases availability and manageability, and another technology lowers availability due additional maintenance windows for cluster failovers. But that’s exactly what you get, when you use MSCS with SCSI bus sharing (RDM or VMFS). A way to address this issue is to use in-guest iSCSI. This means that you access the shared disks directly from the VM due a iSCSI initiator running in the VM. To do so, you have to present the disks for the cluster to the VMs, not to the ESXi hosts. To be honest: In-guest increases complexity. Especially then, when the customer doesn’t have a iSCSI infrastructure. A second method is in-guest SMB, which is currently only supported with Windows Server 2012. Just to clear up the matter with in-guest iSCSI and W2K12(R2):
— Patrick Terlisten (@PTerlisten) February 11, 2014
Mostafa Khalil /VCDX #002) provided the crucial information:
— Mostafa Khalil (@MostafaVMW) February 11, 2014
In-guest iSCSI is supported with W2K12 on vSphere 5.5, which also supportes W2K12 R2 failover clustering. But there’s another interesting fact, that was new to me: Windows Server 2012 failover clustering isn’t supported with ESXi provided shared disks! I found a hint in VMware KB1037959.
Windows Server 2012 failover clustering is not supported with ESXi-provided shared storage (such as RDMs or virtual disks) in vSphere 5.1 and earlier. For more information, see the Miscellaneous Issues section of the vSphere 5.1 Release Notes. VMware vSphere 5.5 provides complete support for 2012 failover clustering.
This means, that you can run Windows Server 2012 failover cluster on vSphere 5.1, but only with in-guest iSCSI or in-guest SMB.
What’s new in vSphere 5.5?
Windows 2012 R2 failover clustering is now supported. But much more significant are changes regarding the storage protocols. With vSphere 5.5 RDMs (shared disks for quorum or data) can be on iSCSI and Fibre Channel over Ethernet (FCoE). Until vSphere 5.5 only Fibre-Channel (FC) was supported. iSCSI and FCoE are supported for cluster-in-a-box (CIB) and cluster across boxes (CAB). Just to make it clear: NFS isn’t supported. Neither for RDM nor for VMFS! Furthermore software and hardware initiator, and mixed setups are supported for iSCSI and FCoE. With vSphere 5.5 the VMW_PSP_RR can be used for the RDMs. There’s no need to change the PSP for the RDMs. VMware KB2052238 summarizes the changes in vSphere 5.5 together.
Clusters are never an easy thing. The complex support matrix does not make it easier. If you’re using Microsoft clusters, be sure to check the above mentioned knowledge base articles before you make a update of your vSphere enviroment or of your Microsoft cluster.
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