Following up on my four-part seriesEnabling Next-Generation Virtual Delivery Infrastructures for the Modern Data Center,” this article explains how Sanbolic Melio helps Citrix XenDesktop and XenApp customers maximize the value of their virtual desktop and application delivery infrastructures.

With it’s unique and extensive capabilities, Sanbolic Melio provides Citrix VDI customers with numerous benefits that have a direct and favorable impact on overall solution cost, including:

  • Streamlined data (server and desktop OS image files) and storage administration
  • Significantly reduced storage capacity requirements and improved storage utilization
  • High availability of XenApp server and desktop OS images, databases and user profiles
  • Seamless infrastructure scale-out (add more servers and/or storage “on the fly”)
  • Exceptional virtual desktop performance (striping (RAID0), QoS, flash and SSD support, “intelligent” data placement, user-defined data tiering)
  • Uniform (farm-wide) image protection via cluster-aware snapshots
  • Enhanced fault-tolerance (resilient file system with no single point of failure, data mirroring (RAID 1, 10, 5, 50, 6, 60))
  • Simple and cost-effective (multi-site) disaster recovery
  • Reduced infrastructure cost and complexity (enables converged/hyper-converged infrastructures)
  • Hardware agnostic (works with industry-standard (commodity) compute and storage hardware)
  • Supports physical, virtual and cloud-based instances.
  • No per-feature licensing costs (includes extensive storage management capabilities and advanced data services enablement)

For This Article We’re Going to Focus on Streamlined Data and Storage Administration

In particular, we’ll discuss how Melio helps Citrix VDI customers take advantage of Provisioning Services (PVS), an integral component of XenDesktop and XenApp, to provision their virtual desktop and application delivery infrastructures.

Using Melio with PVS, administrators can create, manage, maintain, and deliver XenApp server and desktop OS images (vDisks) to tens of thousands of devices with minimal time and effort while enabling the high availability (HA) feature of PVS.

Note: The PVS HA feature allows devices to remain connected to vDisks during server, storage or network failures, thereby ensuring user productivity is maintained during unexpected outages.

Before we discuss how Melio helps customers realize these benefits, let’s review the two methods for deploying PVS in HA mode:

  1. Decentralized HA (relies on replication)
  2. Centralized HA (requires shared storage)

Decentralized HA Model

This model entails the use of replication and requires that a copy of each vDisk be placed on a local (NTFS-formatted) drive on each PVS server. This means that if you have two servers in your PVS farm and you create a new vDisk, you have to copy the vDisk to the second server. And when you make changes (i.e., OS updates, anti-virus updates, add/remove applications, etc.) to the contents of the vDisk, you have to copy the (updated) vDisk to the second server (again).

In environments with only two PVS servers and less than a handful of vDisks, this approach may prove adequate for some. Of course, if this small environment were to grow (to support additional XenApp servers and desktops) and more PVS servers were needed to provide HA and ensure efficient load-balancing of vDisks, this option would quickly become both unmanageable and inefficient as every vDisk would have to be stored on every PVS server, resulting in a significant waste in valuable storage capacity.

Think about it… if you have three PVS servers in your farm and five vDisks (each at 60GB), instead of using just 300GB (5 x 60GB) of disk capacity, you’d have to use 900GB (5 x 60GB x 3 PVS servers) or almost 1TB. Talk about a waste of storage (and money)! Not to mention the additional data management overhead introduced by having to copy or replicate updated vDisks amongst the PVS servers to ensure the vDisks are synchronized across all the servers at all times.

And let’s not forget about protecting all those vDisks, which becomes more challenging as well. Rather than creating a single snapshot of all the vDisks on one drive, you’d have to create and maintain multiple snapshots (one for each drive) to ensure vDisk consistency throughout the entire PVS farm.

In summary, replication introduces additional data and storage management overhead, inefficient use of valuable storage resources (which drives up deployment cost), and unnecessary steps to protect image files. What’s more, scaling out the infrastructure only exacerbates these issues, detracting from the fundamental value of PVS (centrally creating, managing, maintaining and delivering image files) for XenApp and XenDesktop VDI deployments.

Now let’s take a look at the “Centralized HA” model, which requires shared storage, either file-based (CIFS/SMB) or block-based (Sanbolic Melio).

CIFS/SMB-Based PVS HA Deployments

Simply put, using a file share hosted by a file server to enable PVS HA results in a single point of failure, severely limited performance and virtually no scale-out, while a hardware-based file-serving solution such as a NAS appliance introduces proprietary (island) storage management, limited scale, vendor lock-in and a fairly hefty price tag, particularly if multiple appliances need to be clustered in order to scale out a PVS implementation. In addition, using file shares to enable high availability of vDisks across PVS servers located in different data centers (for disaster recovery) can introduce significant performance issues, oftentimes requiring customers replicate vDisks between data centers in order to minimize performance implications.

Melio-Based PVS HA Deployments

Using Melio, customers enable PVS HA and load-balancing while avoiding the challenges and limitations associated with replication and file shares/NAS. This is accomplished by consolidating PVS servers onto a single pool of flexible, scalable, highly available storage that can be accessed (read-and-write) by all PVS servers in a farm concurrently, regardless of whether the servers reside in a single site or in multiple sites (geo-distributed data centers). In addition to enabling vDisk HA and load-balancing, vDisk management and maintenance is greatly simplified and the capacity needed to store vDisks is significantly reduced, lowering storage-related costs dramatically.

Many customers also store their desktop write cache files on Melio shared volumes, further leveraging the investments in their block-based storage to provide the performance necessary to support the potentially intense IO demands typically encountered in mid- to larger-size VDI deployments. With both vDisks and write cache files being highly available, customers achieve a flexible, scalable and robust platform for the provisioning of XenApp servers and virtual desktops throughout their enterprise environments.

It’s important to note Melio is server, storage and hypervisor agnostic, which means all the benefits sited above can be achieved using any make and model server and storage hardware, external (SAN) or internal (server-side) storage, as well as any storage protocol (iSCSI, Fibre Channel, FCoE, shared SAS, etc.), helping VDI customers avoid vendor lock-in.

Here’s How Easy It Is To Create Shared Storage Using Melio:

  1. After provisioning and presenting block storage to all the PVS servers in the farm, an administrator installs Melio on each server and opens the management dashboard (on one of the servers).
  2. The administrator selects the option to create a new volume, assigns it a label and drive letter, drags-and-drops one or more disks (external or internal) onto the new volume, and clicks “Save” to create the shared volume.
  3. The administrator activates the volume with their license key to make the volume accessible to all the PVS servers in the farm.

Once the shared volume is mounted on all the PVS servers, a data store is created in the PVS Administrator console for the vDisks and (optionally) write cache files and the “load-balancing” feature is enabled within the properties of each vDisk. Operating in HA mode, the PVS servers work together to stream vDisks on the shared volume to XenApp servers and virtual desktops.

By avoiding the challenges and limitations associated with replication, file shares and NAS, customers using PVS to provision their virtual desktop and application delivery infrastructures are able to take advantage of its inherent (centralized) benefits rather than diminish them.

In future articles we’ll discuss how Citrix VDI customers leverage Melio’s unique and extensive capabilities to realize other significant benefits, including improving virtual desktop performance, enabling cost-effective DR, and ensuring database and user profile high availability.

For more information about Sanbolic and the Melio software, visit