VMWare VSphere 5 Cluster - what is the best way to connect a large file store LUN to a guest VM on a SAN?

Posted on 2012-09-18
Last Modified: 2012-09-22
I have a VMWare VSphere 5 cluster with:

(3) Hosts with (10) NICs in each, 64 GB of memory in each
(1) Dell Equallogic SAN
(2) Storage switches for the dedicated iSCSI LAN

One of the guest VM's has a large file store (1TB) that is currently being hosted as a pass-thru disk on a Hyper-V this configuration, the file store is a LUN on the same Dell Equallogic SAN that hosts data for the VMWare cluster.  We are migrating the Hyper-V VM's into the VMWare cluster, and the last VM to get migrated is this file server.  The Hyper-V configuration has this file store LUN as a pass-thru disk that is a storage resource in Windows Failover cluster manager.  This LUN is configured to be a physical disk that is passed-thru into the Hyper-V guest through Hyper-V manager (standard pass-thru storage configuration for Hyper-V)..

What is the best way to present this LUN to the VMWare guest VM once we import the Hyper-V guest VM into VMWare?  Should we:

1.  Add the file-store LUN to VMWare storage resources by connecting to it in iSCSI software adapter, and assign that storage to the file-server guest VM?
2.  Add pass-thru NICs into the file server guest VM that connect to a vSwitch and VMKernel on the storage network, and configure the guest VM (Windows 2008 R2 standard x64) to make iSCSI connections to the LUN on its own?
3.  Is there another way to do this that is not described?
Question by:jkeegan123
    LVL 116

    Expert Comment

    by:Andrew Hancock (VMware vExpert / EE MVE)
    1 & 2 are methods you can use.

    But there is a third option where you can present the existing LUN with data to a Virtual Machine it's called RDM (Raw Device Mapping). (very much the same as Hyper-V)

    see here
    LVL 10

    Accepted Solution

    As I interpret your description, #1 only works if you're thinking of it like the pass-through optin on Hyper-V. That's the RDM option that Andrew mentions (not a third option), and is one way to keep the data on the volume intact. Make sure you follow rules for proper connections (NIC-vmkernel port isolation) and user the HIT kit for best performance. If you don't set it up as an RDM, vSphere can't use the existing filesystem and will want to replace it with VMFS5 so it can store virtual disks (VMDKs) & other VM files instead of your data.
    The #2 option also works well, but because VMware sees this traffic as just more data traffic (it doesn't know it's storage traffic), you'll want to use multiple vNICs (and the HIT Kit) in the guest to get better throughput to the guest.
    Your first two options are fastest to implement: you'll have some downtime as you move the VM to vSphere, but reconnecting the existing volume is pretty easy.
    The third option is to go through the process of migrating the data off the volume and on to a VMDK (hosted on another volume). Given the quantity of data, that could be a lengthy process, and you might not have sufficient storage on the array to support that. However, you also have the opportunity to repartition the file store into smaller chunks, in the event the data is amenable to it. Once you have the data on VMDK(s), you gain a lot of functionality in the vSphere environment

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