VMware users are thinking long and hard about ways to offset the increased costs that may come with the new vSphere 5 licensing model.
When VMware announced
Under the old model, a two-processor server running Enterprise Plus would have required two $3,495 licenses, regardless of how much RAM was installed and used by its virtual machines (VMs). Now an Enterprise Plus license grants only 48 GB of allocated RAM per CPU; anything above that -- a common scenario -- requires the purchase of additional licenses.
With hosts containing 256 GB of RAM becoming commonplace, some users expect to have to double the number of licenses they have just to upgrade. And users with highly consolidated environments are therefore actively thinking about ways to mitigate costs.
The RAM party is over
One thing is clear: Under the new model, you can’t take memory for granted any more, said Rod Gabriel, IT infrastructure engineer at UFS, a Wisconsin financial services company.
“RAM used to be free, so to speak,” Gabriel said.
IT architects would max out their VMware hosts with memory, knowing full well that they would run out of RAM well before they ran out of CPU. Instead, with the new vSphere 5 licensing, Gabriel said he knew of IT shops that had cancelled purchase orders for memory-heavy servers.
The vRAM licensing model hasn’t negatively affected Gabriel’s own shop -- yet. With 96 GB of RAM on its dual-processor Cisco Unified Computing System B250 blades, the financial services firm is well within its vRAM entitlement. But the new licensing is making Gabriel reconsider his plans going forward.
“I’d been thinking about doubling the RAM on existing hosts and buying new hosts with 192 GB of RAM,” he said.
Those plans are on hold, pending review.
Bye-bye memory oversubscription?
Another change that the new vRAM licensing model will affect is how people allocate memory to guests.
VMware admins have long relied on vSphere’s memory oversubscription capability, both for technical reasons -- to take the hard work out of sizing a VM -- but also as a means of making virtualization more palatable to application owners.
With memory oversubscription, it’s possible to assign more memory to a guest than it actually uses. Thus, the Exchange administrator feels good that his Exchange VM has 8 GB of RAM assigned to it, while the vSphere administrator feels good because the guest is only actually consuming 4 GB, for example.
For the most part, memory oversubscription is a widely used practice that VMware has in the past used to differentiate its product from the competition. But vSphere 5 counts allocated memory -- not actual memory usage -- against a vRAM allotment, raining on the memory-oversubscription parade.
“We’ll probably pay closer attention to over-allocating memory,” Gabriel said.
Bob Plankers, a virtualization architect for a large Midwestern university, surmised that vSphere could probably calculate its vRAM allotment based on actual RAM usage, not allocated RAM, but that it would be confusing, because it is so dynamic. Instead, he predicted that many administrators would turn to third-party tools to help properly size their VMs for optimal RAM usage.
“I know the vendors like VKernel and Veeam are ecstatic about this,” Plankers said.
Tapping underutilized RAM
If a VMware admin is facing an additional license purchase to accommodate the shop’s memory needs, he or she should first look around for underused memory, said Mark Vaughn, an IT consultant and vExpert.
One obvious thing to do is to power down VMs, Vaughn suggested, because the new licensing rules only apply to VMs that are powered on. There are no easy ways to see VMs that are good candidates for being shut down, but features in vCloud Director can help administrators identify VMs that they haven’t accessed in a while, he said.
Another easy way to add to your vRAM pool is to take advantage of vCenter’s Linked Mode feature. Introduced in vSphere 4, this feature links vCenter domains, providing a single pane of management glass. And linked vCenter domains have the added benefit of pooling their vRAM entitlements, Vaughn said.
Vaughn has long recommended using vCenter Linked Mode for its administrative benefits, but in light of the new licensing, more users will take advantage of the feature, he predicted.
Disaster recovery (DR) environments are also a natural place to look to free up additional vRAM entitlements -- especially those that utilize powered-off VMs, Vaughn added. And in a roundabout way, the new vSphere 5 licensing might actually encourage additional VMware DR deployments, with the additional incentive of increasing vRAM available to a central pool.
Virtualize with care
The “the more you spend, the more you save” argument might work for some, but other shops are thinking about scaling back their use of virtualization, not doing more.
Take test and dev, for example. Under the old unlimited RAM model, “you could spin up a test and dev environment with realistically no additional cost,” Gabriel said. Now, suddenly, “there’s a cost factor to consider, and you really start to think about how you use vSphere,” potentially looking at other virtualization platforms, he said.
At the other end of the spectrum from test and dev, some shops are rethinking plans to virtualize tier-one applications, such as databases, because of their onerous memory requirements.
In an oft-cited example, vSphere 5 now supports VMs with up to 1 TB of memory, but it’s unlikely many shops would deploy that kind of VM, given the licensing overhead they would incur.
“People can forget the hype about a VM with 1 TB allocated memory, as it would be much more cost effective to run that server as a physical host,” wrote blogger Rynardt Spies. “Allocating 1 TB vRAM to a VM will require you to have 22 Enterprise Plus licenses, and at a cost of almost $78,000. I can't see anyone being stupid enough to do that!”
Granted, VMs with 1 TB of memory are a corner case, but many IT professionals report an increasing number of VMs with 24 GB and 48 GB of RAM assigned to them (typically databases, messaging and content management applications). Rather than virtualizing them, running these applications on bare metal might be the simplest way to keep vSphere 5 licensing costs in check.