In the last post of this series we discussed the various software components to purchase, install, manage, patch in a Hyper-V infrastructure. Now I want discuss the all important data storage options.
As is the case with VMware, for automatic high availability failover among Hyper-V hosts you need some form of shared storage system and storage network, most commonly an iSCSI SAN with redundant controller hardware RAID, multi-path iSCSI networking etc. Until recently, shared block storage (SAN) was the only option but Microsoft does now support shared file storage when using their newest SMB 3.0 (server message block) storage protocol available in their most recent server OS’s. To use this you would basically have to install a pair of recent Windows servers with SMB3 support, in a cluster of their own, sitting in front of a SAN or shared SAS storage so this is definitely NOT about simplification. With respect to the complexity of external shared storage for Hyper-V, everything I’ve said about VMware in previous posts of this series applies as well, a separate console to manage and monitor storage, multi-step storage provisioning starting at the array creating targets and luns, connecting to those on every host, initializing disks, formatting file systems, etc. And just like with VMware, you are introducing multiple independent components with different software and firmware versions that have to certified together for interoperability (see the Windows Server Catalog), patches have to be coordinated carefully and of course when there are problems you may need to involve not only Microsoft but the server and storage vendors as well.
Shared storage isn’t always necessary with Hyper-V. In small, simple environments that don’t need automatic failover between hosts, Microsoft offers a feature called Hyper-V Replica that does snapshot based replication of VM’s from one Hyper-V host to another. In some cases this can be a good enough and lower cost option for customers who have smaller data sets and lower RPO and RTO requirements (recovery has to be done manually). The cost however quickly escalates due to the combination of local hardware RAID to protect against inevitable disk failures used in combination with that replication process (not to mention storage space for snapshots and backup storage). Say you have 2 hosts with 5TB of RAW storage each configured with RAID 10 for redundancy with optimal performance characteristics. That 10TB total storage is reduced down to somewhere just over 1TB of truly usable VM storage per host if you are replicating data between hosts. First, RAID10 cuts 5TB RAW on each host down to maximum 2.5TB usable space, but you can’t fill it all up as you must allow free space or a spare to recover from a disk failure. If that “writable” space is used half for “live” VM’s and half for replica storage you basically can store just over 1TB of actual work data per server and the rest of your capacity, 80% is used for redundancy and overhead … and this same math applies using Veeam or other replication software on VMware. For other than these very small, two host environments, this is why shared SAN / NAS storage or fully hyperconverged systems like HC3 are used. In the case of HC3, that original RAID 10 is actually performed across multiple nodes of the cluster so not only is that data redundancy protecting against disk failures, you can actually sustain a full host failure and continue with full data access because the data mirrors are distributed across completely independent servers (not just across disks inside the same box.)
On core hypervisor differences, there are plenty of other sites and blogs that will compare the speeds and feeds and limits of VMware ESX vs. Hyper-V vs. KVM or other open source hypervisors so I won’t do that here. What I will say is that for that overwhelming majority of the market (unless you need single VM’s with 2TB RAM or some outlier requirement like that), none of those things matter, the hypervisor is a commodity with the vast majority of the “heavy lifting” being relegated to the “VT extensions” in the CPU’s themselves. Almost any application you can name will run just fine on almost any hypervisor and the differences mainly come down to the management functionality around the hypervisor (included or purchased from 3rd party vendors) and the total overall cost over the lifetime of the solution.
So that brings us back to cost, or the perception “Well hyper-v is free and included with Windows.” As discussed above, the overall solution is certainly NOT free or included but some people mistakenly believe or assume there is some “discount” on core Windows licensing if you use Hyper-V as the hypervisor. That is absolutely not the case and your cost of licensing Windows server to run in VM’s is exactly the same per host regardless of what virtualization platform you are running Windows on (of course the extra licenses for running SCVMM, vCenter server and their SQL databases are additional). Most customers running server virtualization license Windows Datacenter edition for each virtualization host allowing them to run an unlimited number of virtual machines and move or migrate those VM’s between host without concerns over license counts or frequency of license re-assignment. There are other licensing scenarios that may come into play but no hypervisor will let you legally take that Windows OEM license that came with your brand X server hardware and P2V it into a VM using that hardware specific OEM license. While the flavor of hypervisor doesn’t matter when it comes to Windows licensing, technologies like HC3 hyperconvergence with integrated management and optimized storage performance can help reduce Windows licensing costs by letting you run more VM’s on a smaller number of physical boxes and creating a single “private cloud” type of infrastructure verses multiple independent islands to manage.
In the next and final post of this series I will summarize this series and put forth some simple rules and guidelines that SMBs should consider when looking at virtualizing their infrastructure.
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