Published: November 12, 2007   |   Updated: February 25, 2008

In a virtualization environment, the infrastructure must be able to provide large amounts of storage space to support many different VMs. Fortunately, many options exist for scaling storage based on overall workload requirements. Step 12 presents considerations for designing the storage infrastructure for server virtualization.

Infrastructure storage planning consists of two primary considerations: planning for performance and planning for capacity.

Task 1: Plan for Performance

The goal of designing storage to meet disk performance requirements is to support the required number of IOps. This information was collected in step 2 and totaled in step 6 to arrive at the total disk performance requirement.

In this task, calculate the IOps requirements for each physical server by totaling the IOps requirements for each application on each server. This will give the IOps requirement per server because each host server may be connected to a different storage system. The choice of disk redundancy levels such as RAID 1 or RAID 0+1 affects the IOps calculation. By mapping this IOps requirement to the selected type of disk subsystem and the drive characteristics of that subsystem, it is possible to determine the number of actual drives required to achieve the performance objectives. Remember to consider host-based activities in your planning such as the impact of backup operations on disk performance as well as adding an appropriate buffer to protect the system in the event of any system performance anomalies.

Task 2: Plan for Capacity

In this task, calculate the disk capacity requirements for each physical server by totaling the capacity requirements for each application on each server plus the space that backups need (if any). Doing so gives the disk capacity requirement per server because each host server may be connected to a different storage system.

Redundant Arrays of Independent Disks (RAID) can be used to provide fault tolerance and to improve performance of disk arrays. Common RAID options for production virtualization host servers include RAID 1 (Disk Mirroring), RAID 5 (Disk Striping with Parity), and RAID 0+1 (Mirror Stripe Sets). Each option offers a different portfolio of capacity, performance, and cost.

By mapping this disk capacity requirement plus the RAID configuration to the size of disks in the selected subsystem, it is possible to determine the number of actual drives required for performance.

Note   The actual number of disks required is the greater of the number determined in Task 1 (performance) and the number determined in Task 2 (capacity). Usually that will be the number determined by performance.

Task 3: Select an I/O Form Factor

A primary challenge of implementing a storage infrastructure is maintaining manageability. When working with local storage, a typical data center can include hundreds of individual hard disks and storage volumes. The result is increased management effort and wasted disk space (because of unused storage resources on each computer). Using network-based storage solutions, organizations can centralize their storage management by storing data on the network.

The choice of the form factor for the storage system should reflect the ability to provide the performance and capacity requirements as well as clustering support, if applicable, and VSS snapshot backup capabilities, if required.

Additional Reading

• The TechNet Webcast Working with the VHD File Format in Virtual Server 2005 (Level 3000) at https://msevents.microsoft.com/CUI/WebCastEventDetails.aspx?culture=en-US&EventID=1032284293&CountryCode=US provides details on the different VHD types available in Virtual Server 2005.
• The Windows Server TechCenter article, “Creating virtual hard disks in Virtual Server,” at https://technet2.microsoft.com/windowsserver/en/library/c1726ff8-ea2b-41b1-8cc8-7ec5848d813e1033.mspx?mfr=true provides details on the architecture of different VHD types in Microsoft Virtual Server.
• The white paper, “Using iSCSI with Virtual Server 2005 R2,” at https://www.microsoft.com/downloads/details.aspx?FamilyID=d112aa63-a51e-4722-a41b-98b3ab3700a3&displaylang=en provides information on using iSCSI initiators in a Virtual Server 2005 environment.
• The Microsoft TechNet article, “Using a storage area network with virtual machines,” at https://www.microsoft.com/technet/prodtechnol/virtualserver/2005/proddocs/vs_deploy_SAN.mspx?mfr=true provides information on SAN design for a virtual infrastructure.