Disk Requirements

There are no specific disk requirements for virtual machine disks used with Lync Server 2010. The only consideration is to allocate enough space for the operating system installation and Lync application installation. For Back-End database servers, the same planning figures apply for database sizing. This also applies to the Monitoring and Archiving database size planning figures.

Disk Types

When creating a virtual machine, options exist to create a hard disk for the VM as a fixed size or dynamically expanding. In VMware, the dynamically expanding disk is referred to as thin provisioning. The difference is that with a fixed-size disk, the space allocated to a virtual machine is immediately accounted for on the host operating system disk volume. For instance, if the host has 500 GB of free disk space and a 100 GB fixed size disk is created, the host will reflect 400 GB of free space. Dynamically expanding disks differ in that a maximum size is specified that the disk can grow to, but the space is not immediately consumed. Continuing the previous example, the virtual machine still believes it has a 100 GB hard disk, but space on the host physical disk is consumed only as the virtual machine begins to write data to the disk. The virtual disk is negligible at first, but it might consume 10 GB of space after an operating system is installed, and more when applications and data are added.

A third type of option in disk configuration for virtual machines is to use pass-through disks. Pass-through disks present a physical hard disk directly to a virtual machine. This configuration is not as typical for small environments, but where performance must be guaranteed, and resources not shared with other virtual machines, pass-through disks are an attractive option.

In earlier versions of virtualization products, the rule of thumb was that fixed-size disks yielded significantly greater performance for a virtual machine. With the most recent releases from both Microsoft and VMware, this notion has shifted quite a bit and dynamically expanding disks are now nearly equal in performance after they have been initially expanded. This means that the first time an application writes to a virtual disk, a fixed-size disk will be quicker because a dynamically expanding disk has to first grow the disk before writing the data. At the point where the dynamically expanding disk no longer is growing in size though, the performance is nearly equal.

For SQL Servers, the Microsoft SQL Server team recommends using either fixed-size disks or pass-through disks, so it might make sense to use these types for a Back-End Server.