Multipath I/O (Mpio) - Aberdeen AberNAS 120 Manual

Microsoft® Windows Storage Server 2003 White Paper
Although many vendors provide NAS appliances preconfigured with RAID, system administrators
might want to use VDS to customize the storage solution to meet specific data storage needs,
whether relating to capacity, performance or data protection.
VDS can also be used to attach a NAS device to a back-end SAN. These NAS "heads" contain only
the file serving capabilities; for highly scaleable and highly available pooled storage, they plug into a
Fibre Channel SAN. Each storage unit on the SAN must have its storage configured and made
accessible to the appropriate servers only. Since it is common for storage on the SAN to be from
multiple hardware vendors, prior to Windows Server 2003 and Windows Storage Server 2003 it was
necessary for the system administrator to configure each device using a vendor-specific storage
management application. Not only did this mean using hardware-specific management utilities, it
frequently meant that the system administrator had to physically go to each storage device to do each
configuration.
Windows Storage Server 2003's Virtual Disk Service helps alleviate these administration complexities
in a NAS backend SAN configuration by providing a single management interface for multivendor
storage devices. The system administrator can manage all storage devices directly from a single
management console, and query and configuration operations are common across all managed
devices.
In this scenario, VDS functionality is enabled through hardware vendor support. Each hardware
vendor must supply a VDS "provider" for the storage hardware. The hardware provider translates the
VDS standard APIs (application programming interface) into instructions specific to the storage
device. With communication enabled between the Virtual Disk service and the storage hardware, the
system administrator can now use a single storage management interface to communicate with
multivendor storage devices.

Multipath I/O (MPIO)

Multiple or redundant paths between storage devices and the systems that use them enable
persistent data availability and high I/O performance. In essence, these technologies provide for an
alternate connection in case of failure of the primary I/O path, and, optionally, multiple paths to
improve performance or balance loads.
MPIO software included in Windows Storage Server 2003 is not a feature of the operating system,
but is supported through the Driver Development Kit (DDK). Multipathing allows a host to have up to
32 paths to access an external storage device, which facilitates failover and load balancing.
Multipathing technology is critical in ensuring highly available data to businesses. In the past,
multipathing was a solution only available to large scale enterprises; now this high availability solution
is available to any organization using only Windows Storage Server 2003 (and Windows Server 2003)
technologies.
Microsoft's MPIO delivers a standard and interoperable path for communication between storage
products and Windows Server. With a platform upon which multiple third-party storage systems can
reliably interoperate, businesses have greater choice when building a high-quality, highly available
network storage system, and system administrators will have the flexibility to incorporate products
from multiple vendors into a single, interoperable and highly available storage infrastructure.