When Windows Server 2008 R2 service pack 1 becomes available during the first half of next year, Windows admins will get the long awaited Dynamic Memory feature in Hyper-V. That feature has some limitations, however, and IT pros have other wish list items they would rather see first.
Microsoft added live migration, cluster failover and other important capabilities into Hyper-V R2, which launched last October. The lack of memory over-commit, however, overshadowed some of those improvements. So Microsoft introduced its own flavor of memory over-commit, Dynamic Memory, in the Windows Server 2008 R2 SP1 beta this month.
With Dynamic Memory, administrators can configure a range of memory, memory priority and other settings that Hyper-V uses to determine how much memory to allocate to each virtual machine (VM). Without the feature, admins have to assign a specific amount of memory to a VM, limiting its access to resources.
Because memory over-commit is available in competitive products and provides VM density benefits, many Windows admins refuse to use Hyper-V until it provides that capability, said Alan Silverman, practice leader at Atrion Networking Corp., a Warwick, R.I.-based IT consultancy. Once Windows 2008 R2 SP1 includes the memory management feature, he can then offer it to customers as a lower priced alternative to VMware, he said.
But Dynamic Memory is only supported by Windows Server 2003 or newer, Windows Vista and Windows 7, so not every Hyper-V R2 user will benefit from the new feature.
For instance, Lyle Worthington, CIO of Horseshoe Bay Resorts in Texas, uses Hyper-V as a virtual desktop host hypervisor, but Dynamic Memory will be of no use to him because it doesn't support Windows XP or the Linux guests in his virtual environment.
IT pros would also like to be able to apply the Dynamic Memory feature without shutting down VMs. As it is now, admins have to take VMs offline, disrupting service to activate Dynamic Memory settings.
Admins want better VM density, feature management
Hyper-V R2's low CPU support limit remains a major source of aggravation for Hyper-V users that want to fully use multi-core chips. That's the case for Rob McShinsky, a senior systems engineer with Dartmouth Hitchcock Medical Center in Lebanon, N.H.
"As our environment matures, we are looking at expanding our virtualization philosophy from a strict maximum number of VMs per host to also include fewer, more robust VMs utilizing more cores per host," McShinsky said.
Windows Server 2003 only supports two vCPUs and Windows Server 2008 supports four virtual CPUs (vCPU). All other supported guest OSes only support one vCPU, so admins aren't able to pack as many VMs onto multi-core chips as they'd like.
For instance, when Windows Server 2008 R2 lives on a box with dual, quad-core Intel Xeon chips with Hyper-Threading, it appears there are 16 cores. But since Hyper-V R2 only supports up to four logical processors, the most an admin can ever give a VM on that system is 25% of the CPU resources.
Windows admin also want to be able to live expand virtual hard disks (VHDs) to avoid downtime, which they have been doing for years in the physical world with RAID sets.
Microsoft knows what the IT shops want. A company blog post stated that "dynamically" or live expanding VHDs in Hyper-V R2 did improve performance in some areas. But the company still recommends fixed disks for production use to prevent systems from running out of storage.
Microsoft also added into Hyper-V R2 the ability to hot add or remove storage while VMs are running, but Windows administrators want more. One IT pro using Hyper-V R2 said he'd like to see better performance of dynamic disks with reduced administrative maintenance. This would help in overall disk space requirements without loss of performance and no added virtual disk maintenance tasks.
A reduction of disk space utilization or data de-duplication is also on McShinsky's wish list. "As my virtual environments have grown, disk space sprawl has been a growing pain point," he said.
Many Windows administrators said they want Microsoft to advance Hyper-V features beyond what they have already seen from the competition.
"I applaud [Microsoft] for narrowing the gap so quickly, but I would like to see some innovation beyond the reverse engineering of features," McShinsky said.