Virsto One is the first and only hypervisor-based storage virtualization software that is built from the ground up for the specific needs of virtual datacenters.
Flawed Assumptions = Flawed Solutions
When it comes to storage, virtual servers work pretty much like physical servers, right? Absolutely correct. Emphasis on the pretty much. There are subtle, but crucial differences that make all the difference.
For example, physical servers have a direct one to one correspondence with their operating systems. In the virtual world, servers becomes software objects with much more complex relationships, and new servers (VMs) are created as clones of golden images. As such, provisioning in the virtual world becomes management of large software objects that share ancestry and a great deal of common data. This is just one way in which the virtual server storage use case is dramatically different from physical servers. There are quite a few other differences, some of which are shown in the chart below.
These issues are not specific to any brand of hypervisor; they are inherent in the nature of virtualization. The unique problems of virtual servers are what Virsto One is designed to address. Virsto One is unique is its ability to provide for virtual environments enterprise class storage features at a fraction of the cost of alternatives.
In this discussion, we use terminology specific to Microsoft Windows Server 2008 R2 Hyper-V, because that's the platform supported by the initial release of Virsto One. However, note that Virsto One has been architected to be hypervisor (and storage) agnostic.
Simplicity, well integrated
Virsto One is hypervisor based storage virtualization software that installs in the parent partition of Microsoft Hyper-V. From the server administrator's point of view, Virsto One is incredibly simple and integrated into Hyper-V management.
Virsto One is a 10MB standard Windows package, and takes only seconds to install. Configuring Virsto One means designating a master for cluster-wide metadata management (once per cluster) a log device (once per physical server), and choosing storage volume(s) for Virsto VHD placement.
Once configured, using Virsto One is as simple as using Microsoft Hyper-V Manager and PowerShell, because Virsto One is fully integrated with WMI and its UI is an MMC snap-in.
The Virsto One solution is also extremely easy to configure and manage using standard Microsoft technologies like WMI, Powershell and VHDs.
Specifically, we realized that storage architectures lagged behind their server counterparts in the virtualized data center. This enabled the building of the Virsto One architecture definition and product implementation details. Virsto One is a software only product, an instance of Virsto One is installed on each physical server in the data center. No modification to the guest VM is required. (Virsto supports any block storage device technology and can operate in any mix of iSCSI, Fibre Channel, SAS, etc). In a clustered environment all storage must be accessible to all servers to support live migration and high availability.
The guest VMs are presented with virtual disk images. Virsto One manages the allocation and placement of the virtual disk content on available storage devices. In a Virsto One enabled data center, a storage device is configured only once at initial installation time. All operational provisioning is done through the Virsto One interface.
Internally, Virsto One uses techniques similar to high performance relational databases by journaling I/Os from individual VMs and then coalescing for storage at their permanent location. This technique of sequentially writing and storing write I/Os addresses many of the performance and storage problems associated with VM environments plus it offers new options for users to grow and better management going forward.
Below is a drawing of the Virsto One architecture, showing internal components of one physical node, or server. The three main components are: the system service, filter driver and the virtual hard disk (VHD).
The Virsto One software installs into the parent partition of the hypervisor, in this case, Microsoft Hyper-V. Virsto One consists of a filter driver and a system service. The Virsto service talks directly to standard windows management interface (WMI). And therefore accessible by any compatible WMI service, including Powershell and Microsoft Management Console (MMC). Virsto One integrates as a snap-in for Microsoft Hyper-V manager’s graphical user interface.
The filter driver resides above the raw volume layer and presents a virtual disk as a virtual hard drive (VHD) object to the parent partition. Hyper-V manager attaches these VHD objects to guest VMs in a standard manner. Virsto One VHD is a highly performant, thinly provisioned dynamic storage object which conforms to Microsoft fixed VHD specifications. Therefore, Virsto One VHD is automatically compatible with all Microsoft system storage functionality.
The Virsto One VHD should not be confused with a Microsoft dynamic VHD. The Virsto One VHD is thinly provisioned but has none of the poor performance characteristics of the Microsoft dynamic VHD. The Virsto One VHD is a cluster aware object and can migrate between physical machines, following the VM it is attached to.
The architecture components are then used to offer some key technology leverage points for virtual storage environments. Let's look at a few of these technology points in depth.
Snapshots and Clones
In the virtual world, software objects are replicated, copied, cloned, backed up and restored in an extremely dynamic matter. These objects are no longer tied to a specific piece of dedicated hardware. The main provisioning method for virtual servers is cloning, cloning of a template or a ‘golden image’. Cloning is extremely powerful. If not implemented correctly, cloning will lead to VM sprawl. In our architecture, clones became the rule, not the exception.
The relationship between snapshots and clones is vital for being able to offer benefits around 'golden images'. Virsto One allows for unlimited high performance snapshots. A snapshot is a recorded state of a virtual disk or a group of virtual disks at a point of time. Creation of a snapshot is almost instantaneous and irrespective of the virtual disk size. Multiple virtual disks can be included in a single snapshot. Multiple snapshots can be maintained indefinitely with no performance impact.
In order to access content of a snapshot, a associated virtual disk object must be created. This virtual disk object is called a clone. When created, a clone shares the data blocks with the original virtual disk. Therefore, a newly created clone does not take any additional disk storage space. As the clone is written to, only the new writes or updates are stored.
Using snapshot and cloning to provision operating system images saves a huge amount of space compared to traditional methods. Snapshots and clones are cluster aware and can be accessed and managed by any server in the Virsto One enabled cluster.
Snapshots can be created by either a WMI call or under control of Volume Shadow Service (VSS). A Virsto One VSS provider is part of the product distribution package and provides for easy integration with all major backup software.
Clustering
Clustering is no longer an option for the virtualized data center, it is a requirement. Virtualization introduces the unique ability to live migrate running VMs, but this would not be possible without the underlying support of the storage infrastructure.
Virsto One supports live migration of virtual machines. During migration, control of the virtual disk image is transferred from the source physical server to its destination. This is done transparently and is integrated into the management infrastructure. Virsto One does not depend on any specific cluster architecture and is compatible with existing cluster frameworks.
Management
Virsto One integrates into the Microsoft Hyper-V management console. For Virsto One users who prefer to do their own scripting, powershell benefits are also available. WMI enables further integration into applications like MMC (Microsoft Management Console).
Summary
Virsto One is a robust architecture for enabling virtual storage to be as empowering as virtual servers. We look forward to building and leveraging our technology into more features as we expand our virtual storage platform.
