No one has to tell you about your data requirements growing faster than
your capability to manage them. Storage area networks (SANs) have claimed to be the answer. However, SANs have, in some respects, added to the management complexity. On the other hand, storage domain managers can step in to ease the management of a SAN by providing isolation within the SAN.
A storage domain manager device provides a centralized management point for a group, or domain, of storage resources. These resources will include both devices and the content stored on them. The devices being managed will be varied - different media and even different vendors. Virtualization helps to isolate changes on the physical devices side from the hosts using the resources.
The storage domain manager sits right in the middle of a complex SAN
environment. By positioning the storage domain manager, this device can
simplify the entire SAN into two sides: host side and physical side. The
host-side connects hosts to virtual devices presented on the storage domain
manager. This interface allows for additional isolation between hosts using
the storage resources in the domain.
On the other hand, the physical-side connects all of the physical devices into the storage domain manager. These devices are pooled and then based on policies that can be used by the hosts connected to the host-side of the storage domain manager. Since the connection from the host-side to the physical-side occurs within the storage domain manager, you can make changes on one-side and not affect the other. Additionally, you can affect the configuration for a specific host without having to modify the rest of the hosts in the storage domain.
You could use several alternative architectures for creating a storage
domain manager - server-based, meta server, and network-centric. The
server-based version is a software application that is distributed throughout
the storage domain to coordinate storage access. This approach is simple of
the surface, but as system complexity grows, the architecture gets
exceedingly difficult to manage. Each server in the storage domain becomes an administration point - making the storage management problems worse. The meta-server architecture uses a server dedicated to performing control
operations. This architecture is attractive becomes it doesn't impact the
data-path itself. The flip-side is that it doesn't control the dath-path
either. Rogue hosts can access storage resources they aren't supposed to
access with either the server-based or the meta-server architectures. For
some applications, the meta-server could become a bottleneck restricting
access.
The network-centric architecture places the storage domain manager in the middle of the data-path. This capability is both an advantage and a
disadvantage. The storage domain manager has the advantage of being
perfectly poised to present a virtual device and restrict access as needed.
However, the data-path performance could suffer.
Elizabeth M. Ferrarini - She is a free-lance writer from Boston,
Massachusetts.
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