Having largely perfected the server side of virtualization, VMware & Microsoft have turned their attention towards improving storage as they recognize the critical role that it plays in a virtual environment. VMware in particular has put a big focus on enhancing storage features in recent vSphere releases and promises to continue that trend in future releases. To understand why storage is getting so much attention now you need to look at the role storage plays in a virtual environment.
If you look at the four basic resources that are required for a VM to function, CPU, memory, network and storage; storage is different from the other resources in two ways. First, the other resources are all local to a host and storage is typically accessed remotely via a network or fabric and I/O has a long journey from the host to a storage device. Secondly, unlike the other resource types, storage is a shared resource by many hosts so there is a lot of contention for it. As a result storage is often the limiting factor to achieving higher VM densities which is why VMware has put so much focus on storage features.
Looking at some recent storage enhancements, there are a few key areas that VMware & Microsoft are focusing on that include integration, management and software defined storage. VMware has been trying to mimic with software many of the features traditionally found inside storage arrays and has also turned towards mimicking an entire array with a virtual storage appliance. Let’s take a look at the top 5 storage enhancements from VMware & Microsoft and their use cases in a virtualized environment.
1 – Storage APIs and integration
Integration between the hypervisor and storage devices is the key to efficiency in a virtual environment. This allows the two to communicate with each other more effectively and also offloads resource intensive tasks from the hypervisor to the storage array which is better equipped to handle them. VMware has a number of APIs that they have developed under the vStorage API family that allow storage vendors to integrate directly with vSphere. The vStorage APIs for Array Integration (VAAI) provide capabilities such as offloading block zeroing and data copy as well as providing a more granular disk locking mechanism. VMware has made enhancements to VAAI to improve thin provisioning management and efficiency by allowing the hypervisor to reclaim disk blocks once data has been deleted. Microsoft has made improvements in this area as well with their Offloaded Data Transfer (ODX) and thin reclaim (UNMAP) capabilities that are built into Hyper-V & Winders Server.
2 – Storage resource controls
Because storage is a shared resource, contention for storage resources can be like the Wild West with many hosts and VMs all fighting over limited storage resources. Having a sheriff in town can help tame that contention and ensure that VMs are getting the resources they need. Features like VMware’s Storage I/O Control (SIOC) allows for centralized storage resource management so storage prioritization can be applied across all hosts connected to a datastore instead of on an individual basis. This can help ensure fairness across hosts so critical VMs get the storage resources they need and you don’t have to worry about one host hogging all the storage resources.
3 – Non-disruptive storage migration
A virtual environment is very dynamic and VMs need mobility to ensure resources are balanced and for increased availability. VMware has had their vMotion feature for years that allows a VM on shared storage to move from one host to another when needed without any disruptions. Microsoft introduced a similar feature which they call Live Migration in Hyper-V 3.0, but unlike vMotion it did not require shared storage. VMware enhanced vMotion when they introduced Storage vMotion which allows a VM to move from one datastore to another without disruption. vMotion and Storage vMotion were two different features that operated independently and at different levels (host vs. storage). VMware finally bridged the gap between the two features in vSphere 5.1 with their latest enhancement informally called “Shared Nothing vMotion” that can move a VM to a different host and datastore in one operation. This was on par with what Microsoft had with Live Migration and provides better VM mobility especially for environments that do not have shared storage and can help make balancing workloads and shifting VMs around for scheduled maintenance much easier.
4 – Virtual Storage Appliances
Virtual storage appliances (VSA) allow you to create a virtual shared storage device from local server disk that can be presented to any host and used in the same manner as traditional physical shared storage (NAS/SAN). While historically known as VSAs, VMware has created a new marketing term for them called Software Defined Storage that is part of their whole Software Defined Data Center vision. Today there are many VSAs on the market both from VMware and other storage vendors that offer different features and capabilities. Microsoft currently does not offer a VSA as part of Hyper-V but there are some 3rd party VSA’s that work with Hyper-V. VSAs can provide many benefits and are suited for many different uses cases. They are great for SMBs that desire shared storage to be able to use the many advanced virtualization features that required shared storage but don’t have the budget for a NAS or SAN device. They are also good for remote office deployments and to implement cost-effective BC/DR.
5 – Storage load balancing
Storage workloads are often very dynamic and unpredictable and being able to shift them around to better balance them helps improve performance and avoid overburdened datastores. VMware has a feature called Storage Distributed Resource Scheduler (DRS) that allows for intelligent placement of VMs that are powered on as well as the shifting of workloads from one storage resource to another whenever needed to ensure optimum performance and eliminate I/O bottlenecks. Storage DRS is similar to the auto tiering feature that is found in storage arrays but instead of working at the disk block level it works at the VM level. Storage DRS works in conjunction with other vSphere storage features, when combined, Storage DRS is the brains, Storage vMotion is the muscle and Storage I/O Control is the judge to help create a more balanced and efficient storage platform for VMs.
As the hypervisor management tools take over and automate more and more tasks, it becomes harder to maintain visibility between the virtual and storage resources. As a result, having good virtualization management and monitoring software for your virtualization and storage resources is critical. Because storage is such an important part of a virtual environment you can’t afford to make any assumptions about your storage resources. Products like SolarWind’s Virtualization Manager and Storage Manager can help you proactively monitor and analyze the performance and capacity of your storage resources. Featuring configurable real-time dashboards you can easily stay on top of storage trends and identify any problem areas that may be occurring. Together, SolarWinds Virtualization Manager and Storage Manager can help you keep a sharp eye on the performance and capacity of your entire physical and virtual storage infrastructure-from VM to spindle!
