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15 Dell EMC PowerVault ME4 Series and Microsoft Hyper-V | 3921-BP-WS
3.3.2 Virtual hard disk type
In addition to the format, a virtual hard disk can be designated as fixed, dynamically expanding, or
differencing.
Virtual hard disk type options
The dynamically expanding disk type will work well for most workloads on ME4 Series arrays. If the array is
configured to use virtual disk groups and pools which take advantage of thin provisioning, only data that is
actually written to a virtual hard disk, regardless of the disk type (fixed, dynamic, or differencing), will consume
space on the array. As a result, determining the best disk type is mostly a function of the workload as
opposed to how it will impact storage utilization. For workloads generating very high I/O, such as Microsoft
SQL Server
®
databases, Microsoft recommends using the fixed size virtual hard disk type for optimal
performance.
As shown in Figure 10, a fixed virtual hard disk consumes the full amount of space from the perspective of the
host server. For a dynamic virtual hard disk, the space consumed is equal to amount of data on the virtual
disk (plus some metadata overhead), and is more space efficient from the perspective of the host. From the
perspective of the guest VM, either type of virtual hard disk shown in this example will present a full 60 GB of
available space to the guest.
Fixed and dynamic virtual hard disk comparison