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Appendix D. Enabling LUN Support in Linux

To verify the detection of a tape drive, administrators should check for its entry in

/proc/scsi/scsi. Current versions of Linux may not scan the logical storage unit

(LUN) ID of every device. This can result in some PowerVault devices not being

identified or listed in the /proc/scsi/scsi output. Administrators can follow these

steps to enable support for such devices.

1. Type cat/proc/scsi/scsi. The output will look similar to the following:

Attached devices:

Host: scsi3 Channel: 00 Id: 00 Lun: 00

Vendor: IBM Model: ULTRIUM-TD3 Rev: 5BG2

Type: Sequential-Access ANSI SCSI revision: 03

2. Identify the host adapter, channel number, target ID number, and LUN number

for the first LUN of the device to be configured. In this example, the Certance

Ultrium 2 (a drive in the PowerVault 124T) is shown at the address, or nexus, 3

0 0 0 — which means host adapter 3, channel number 0, ID 0, and LUN 0. The

PowerVault 124T always has the tape drive at LUN 0 and the robot at LUN 1.

3. For each LUN that needs to be discovered by Linux, issue the following

command: echo "scsi-add-single-device H C I L">/proc/scsi/scsi H C I L

refers to the nexus described in step 2. So, with the PowerVault 124T robot

configured at LUN 1, type: echo "scsi-add-single-device 3 0 0

1">/proc/scsi/scsi. The echo command will force a scan of each device at the

given nexus.

4. Type cat /proc/scsi/scsi again to verify that all devices are now listed. The

output will look similar to the following:

Attached devices:

Host: scsi3 Channel: 00 Id: 00 Lun: 00

Vendor: IBM Model: ULTRIUM-TD3 Rev: 5BG2

Type: Sequential-Access ANSI SCSI revision: 03

Attached devices:

Host: scsi3 Channel: 00 Id: 00 Lun: 01

Vendor: DELL Model: PV-124T Rev: V31

Type: Sequential-Access ANSI SCSI revision: 03

Administrators should add the echo command to the Linux boot scripts

because the device information is not persistent and must be created each time

the system boots up. One example file that can be used for storing the

commands is /etc/rc.local. Note that configuring additional devices on a server

or a storage area network (SAN) can cause the devices to be reordered, which

requires administrators to modify the commands. If the Fibre Channel adapter

supports Persistent Bindings or an equivalent function, it can be enabled to

reduce the chance of devices being reordered upon discovery.

Note:

This procedure must be run each time the server is booted. Also, if

backup application services are running (for example, they automatically

start when the OS loads), they must be disabled and re-enabled after the

above procedure.

The

other way to enable LUN support is to recompile the kernel and enable

LUN scanning in the Adaptec driver, but it requires advanced knowledge of

Linux and will not be covered here. However, it will allow the server to always

boot and see the device without any manual procedures.

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