LUN Scanning on linux
Autor: Lutieri G. B. | Publicado: 2011-09-19T16:14:00-03:00

COPIED FROM
http://support.dell.com/support/edocs/stor-sys/124t/en/124tvs16/install.html#enabling_lun_linux

References:
http://tldp.org/HOWTO/SCSI-2.4-HOWTO/mlproc.html


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.
     Type cat/proc/scsi/scsi.         The output will look similar to the following:
Attached devices:
Host: scsi3 Channel: 00 Id: 00 Lun: 00
&nbsp;&nbsp;&nbsp;Vendor:&nbsp;&nbsp;&nbsp;Quantum Model: DLT VS160&nbsp;&nbsp;&nbsp;Rev:      3100
&nbsp;&nbsp;&nbsp;Type:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Sequential-Access&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;ANSI      SCSI revision: 03        

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.        
For each LUN that needs to be discovered by Linux, issue the  following command:          echo  "scsi add-single-device        H C I L"&gt;/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"&gt;/proc/scsi/scsi          The echo command will force a scan of each device at the given  nexus.

     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
&nbsp;&nbsp;&nbsp;Vendor:&nbsp;&nbsp;&nbsp;Quantum Model: DLT VS160&nbsp;&nbsp;&nbsp;Rev:      3100
&nbsp;&nbsp;&nbsp;Type:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Sequential-Access&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;ANSI      SCSI revision: 03          Attached devices:
Host: scsi3 Channel: 00 Id: 00 Lun: 01
&nbsp;&nbsp;&nbsp;Vendor:&nbsp;&nbsp;&nbsp;DELL Model: PV-124T&nbsp;&nbsp;&nbsp;Rev:        V31
&nbsp;&nbsp;&nbsp;Type:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Sequential-Access&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;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.


This procedure also applies when a new Volume (LUN) is created in a storage system and is correctly mapped to the host. In this case is necessary to ReScan the target to update the LUNs in the OS.

In the former case partprobe can be issued to update the partition table.




&nbsp;keywords: medium changer, linux, 124, TL2000, TL4000, tape device