Installation guide

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EMC Fibre Channel and iSCSI with QLogic HBAs in the Windows Environment
Planning, Miscellaneous Procedures, and Troubleshooting
Understanding Persistent Binding in a Fabric Environment
Persistent binding is the mechanism to create a continuous logical
route from a storage device object in the Windows host to a volume in
the EMC storage array across the fabric.
Without a persistent binding mechanism, the host cannot maintain
persistent logical routing of the communication from a storage device
object across the fabric to an EMC storage array volume. If the
physical configuration of the switch is changed (for example, the
cable is swapped or the host is rebooted), the logical route becomes
inconsistent, causing possible data corruption if the user application
is modifying data through inconsistent logical routing of the
communication from the driver entry point to a volume in an EMC
storage array across the fabric.
The Windows 2000/Windows 2003 operating system (OS) does not
provide a satisfactory means to allow persistent binding. Most
software applications access storage using file systems that are
managed by the Windows OS. (File systems are represented by drive
letters: colons: C:, D:, etc.) For storage devices containing file systems,
Windows writes a Disk Signature to the disk device. The operating
system can then identify, and associate with, a particular drive letter
and file system.
Since the signature resides on the disk device, changes can occur on
the storage end (a cable swap, for example) that can cause a disk
device to be visible to the host server in a new location. However, the
OS looks for the disk signature and, providing that nothing on the
disk changed, associate the signature with the correct drive letter and
file system. This mechanism is strictly an operating system feature
and is not influenced by the Fibre Channel device driver.
Some software applications, however, do not use the Windows file
systems or drive letters for their storage requirements. Instead they
access storage drives directly, using their own built-in “file systems.”
Devices that are accessed in this way are referred to as raw devices and
are known as physical drives in Windows terminology.
The naming convention for physical drives is simple and is always
the same for software applications using them. A raw device under
Windows is accessed by the name \\.\PHYSICALDRIVEXXX,
where XXX is the drive number. For example, a system with three
hard disks attached using an QLogic Fibre Channel controller assigns
the disks the names \\.\PHYSICALDRIVE0,