Virtualization Pro

Feb 25 2009   3:21PM GMT

VSphere features explained: vStorage thin-provisioned disks and the Cisco Nexus vSwitch

Gabrie Gabrie Zanten Profile: Gabrie

If you’re following VMware, then you have probably already read about some of the new functions that the next generation of the VMware Infrastructure 3 product suite, vSphere, will offer. Learning that they’re available, however, and learning how they work are two entirely different ball games, and since I’m at VMworld Europe I had the chance to ask representatives about two new vSphere features: vStorage thin-provisioned disks and the Cisco Nexus vSwitch.


VSphere features a great new feature called vStorage, which enables you to thin-provision your disks in a few clicks. All sys admins are familiar with creating 10 GB disks designed just to hold Windows, because at some point Windows will probably need about 10 MB. But once you’ve provisioned a disk for that amount of space, even if it goes unused, it’s unavailable to the rest of your system. And how often do application admins claim a lot more disk space than they actually need, just to be on the safe side?

With thin-provisioned disks, you don’t lose all that unused space because the space is not seen as used by VMware until the guest actually uses the space by writing to it.

Now the first question that comes to mind is, what about fragmentation? According to the VMware technician I spoke with, it’s not that much of a problem. First, he said that thin-provisioning is not something you would want to use for just any type of workload, i.e. thin-provisioning a heavy SQL database would not be smart.

I have to agree with him there; one should always remember that no matter how brilliant a new technology is, common sense should never be put aside.

Anyway — back to fragmentation. For workloads that are suited for thin-provisioned disks, fragmentation is not that big of an isue since disks grow in 1 MB increments.

The second question on vStorage I asked was: I have a SAN that is already loaded with 90 TB of storage. How on earth am I going to convert the existing disks to thin-provisioned disks? And no, VMware Converter is not an option. We have about 750 running virtual machines and I cannot afford the downtime that I would need to convert all these disks.

Fortunately, he said this can be done in a simple way: simply perform a storage VMotion to a different data store. In the migration wizard there is now an option to migrate the disk to a different data store in order to convert it to a thin-provisioned disk. That’s all there is to it. So if you really need to convert your whole set of VMs you can do it without downtime.

Cisco Nexus vSwitch

Cisco is the first to deliver a vSwitch that integrates with VMware vSphere. This vSwitch will act just like a physical Cisco switch but with a number of features customized for a virtual infrastructure.

Now what I would like to know is how it integrates with vSphere. Is it a plug-in for vCenter? Should you install it in the service console?

A Cisco rep answered both of my questions at the VMworld Europe Cisco booth. The Nexus vSwitch is in every installation of ESX and ESXi, whether you buy the Nexus or not. You need a license key to unlock it and you need the Virtual Switch Management (VSM) module from Cisco. This management module can be retrieved from Cisco in a number of ways: You can download the VSM as a virtual appliance or buy it as a physical hardware appliance.

Once the VSM is set up, it can manage the Nexus Virtual Ethernet modules (VEM) on each ESX host. You can manage each VEM on a per host basis, but the Nexus VEM fully integrates with the distributed switch technique, which means that once configured, it can be automatically deployed to each ESX host in a cluster.

1  Comment on this Post

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  • Rana0Killer
    Hi, I am new to VMware . can you please help ne to understand that how thin provision helps us by leaving unused space as anavailable? Thanks! Rana
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