Server virtualisation--killer app for iSCSI!(Storage Expo 2008)

Author:Cormier, Larry

Server Virtualization is the killer app for iSCSI. While this sounds like just another aggressive sound bite, the reality is that the facts back it up.

Server virtualization implementations began in Test and Development organizations. Mostly in large businesses where existing fiber channel SANs were already in place. As the benefits server virtualization accelerated adoption by smaller organizations, the ease of use and affordability offered by iSCSI motivated end users to implement iSCSI SANs instead of fiber channel for storage. IT managers who are familiar with both technologies began to understand some inherent benefits from using iSCSI as storage for virtualized environments. Over half of our customers are purchasing LeftHand iSCSI SANs in conjunction with some sort of server virtualization project, when asked "why iSCSI instead of FC?" customers had a litany of reasons. I've tried to summarize their responses below.

The hardware-centric nature of Fibre Channel (FC) creates a number of problems when implementing virtual machines. In FC environments WWNs (World Wide Names) are used to uniquely identify equipment in the SAN. The WWN is an identifier tied to specific hardware such as a server HBA or a storage array. In virtualized environments, this dependency on physical hardware intensifies the complexity of managing the environment and exposes new security risks, iSCSI provides a number of advantages in virtualized environments.

  1. iSCSI Simplifies Virtual Machine Mobility for High Availability (HA): Virtualization increases the need for HA. With server virtualization, users typically run multiple applications on each physical server, exposing themselves to a potentially significant impact if a server fails since every single application (all the VMs) running on that server will go down. To solve this problem, virtualization vendors have implemented mobility features that enable VMs to move to other physical servers in the event the server they reside on fails. Using a FC SAN in this type of environment creates additional complexity.

    1. Every VM must be mapped to every FC HBA that could potentially be used as the physical connection to the SAN.

    2. Every FC HBA that a VM may use must have access to that VMs' storage.

    The multiple layers of relationships (VM to HBA to storage) create complexity and make the FC SAN difficult to manage. iSCSI avoids this complexity because it uses an IQN (iSCSI qualified name) on each virtual machine that...

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