EMC QLA22xx, QLA23xx manual Understanding Persistent Binding in a Fabric Environment

Introduction

\\PHYSICALDRIVE0, \\PHYSICALDRIVE1, and \\PHYSICALDRIVE2. The number is assigned during the disk discovery part of the Windows boot process.

During boot-up, the Windows OS loads the driver for the storage HBAs. Once loaded, the OS performs a SCSI Inquiry command to get information about all of the attached storage devices. Each disk drive that it discovers is assigned a number in a semi-biasedfirst come, first serve fashion based on HBA. (Semi-biasedmeans that the Windows system always begins with the controller in the lowest-numbered PCI slot where a storage controller resides. Once the driver for the storage controller is loaded, the OS selects the adapter in the lowest-numbered PCI slot to begin the drive discovery process.)

It is this naming convention and the process by which drives are discovered that makes persistent binding (by definition) impossible for Windows NT/Windows 2000/Windows 2003. Persistent binding requires a continuous logical route from a storage device object in the Windows host to a volume in an EMC storage array across the fabric. As mentioned above, each disk drive is assigned a number in a first come, first serve basis. This is where faults can occur.

Example Imagine this scenario—A host system contains controllers in slots 0, 1, and 2. Someone removes a cable from the QLogic controller in host PCI slot 0, then reboots the host.

During reboot, the Windows OS loads the QLogic driver during reboot and begins disk discovery. Under the scenario presented above, there are no devices discovered on controller 0, so the OS moves to the controller in slot 1 and begins naming the disks it finds, starting with \\PHYSICALDRIVE0. Any software applications that were accessing \\PHSYICALDRIVE0 before the reboot will be unable to locate their data on the device, because it has changed.

The following figure shows the original configuration before the reboot. HBA0 is in PCI slot 0 of the Windows host. Each HBA has four disk devices connected to it, so Windows has assigned the name \\PHYSICALDRIVE0 to the first disk on HBA0. Each disk after that is assigned a number in sequence as shown in the figure.

Understanding Persistent Binding in a Fabric Environment 1-3

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