Emulex 110 Przewodnik Instalacji Pobierz pdf (Strona 229)

Understanding persistent binding

229

Troubleshooting

For example, a system with three hard disks attached using an

Emulex Fibre Channel controller assigns the disks the names

\\.\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

adapters. Once loaded, the OS performs a SCSI Inquiry command to

obtain information about all the attached storage devices. Each disk

drive that it discovers is assigned a number in a semi-biased first come,

first serve fashion based on adapter. Semi-biased means 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. 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 Emulex controller in host

PCI slot 0, then reboots the host.

During reboot, the Windows OS loads the Emulex 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

accessing \\.\PHSYICALDRIVE0 before the reboot will be unable

to locate their data on the device, because it changed.

Figure 164 on page 230 shows the original configuration before the

reboot. Adapter 0 is in PCI slot 0 of the Windows host. Each adapter

has four disk devices connected to it, so Windows has assigned the

name \\.\PHYSICALDRIVE0 to the first disk on Adapter 0. Each

disk after that is assigned a number in sequence as shown in

Figure 164.

1 2 ... 224 225 226 227 228 229 230 231 232 233 234 ... 239 240

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Emulex 110 Przewodnik Instalacji Strona 229