SCSI tapes and medium changers as virtual SCSI devices

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FC-attached SCSI tape and medium changer devices are virtualized as virtio SCSI devices.

To provide high reliability, be sure to set up redundant paths for SCSI tape or medium changer devices on the host. A device configuration for a SCSI tape or medium changer device provides one virtual SCSI device for each path. Figure 1 shows one virtual SCSI device for sg<0>, and one for sg<1>, although these devices represent different paths to the same device. The lin_tape device driver models path redundancy on the virtual server. lin_tape reunites the virtual SCSI devices that represent different paths to the same SCSI tape or medium changer device.

To provide a SCSI tape or medium changer device for a virtual server:
  1. Set up the SCSI tape or medium changer device.

    See Preparing SCSI tape and medium changer devices.

  2. Configure the SCSI tape or medium changer device in separate device configuration-XML files.

    You need to check this configuration after a host reboot, a live migration, or when an FCP device or a SCSI tape or medium changer device in the configuration path is set offline and back online.

    See Configuring devices and Configuring virtual SCSI devices.

Virtual SCSI device configuration topology

Figure 1 shows one SCSI tape and one SCSI medium changer, which are accessible via two different configuration paths. They are configured as virtual SCSI devices on a virtual server.

Figure 1. Multipathed SCSI tapes and SCSI medium changer devices configured as virtual SCSI devices

This graphic shows multipathed SCSI tapes and SCSI medium changer devices that are configured as virtual SCSI devices.

Each generic SCSI host device is configured as a virtual SCSI device.

SCSI device identification

For a SCSI tape or medium changer device configuration, the following device names are relevant:
Standard device name
Standard device names are of the form:
sg<x> for SCSI tape or medium changer devices on the host using the SCSI generic device driver.
IBMtape<x> for SCSI tape devices on the virtual server using the lin_tape device driver.
IBMchanger<x> for SCSI medium changer devices on the virtual server using the lin_tape device driver.
Where <x> can be one or more digits.

They are assigned in the order in which the devices are detected and thus can change across reboots.

SCSI device name
SCSI device names are of the form: 
<SCSI-host-number>:0:<SCSI-ID>:<SCSI-LUN>
Where:
<SCSI-host-number> is assigned to the FCP device in the order in which the FCP device is detected.
<SCSI-ID> is the SCSI ID of the target port.
<SCSI-LUN> is assigned to the SCSI device by conversion from the corresponding FCP LUN.

SCSI device names are freshly assigned when the host reboots, or when an FCP device or a SCSI tape or medium changer device is set offline and back online.

SCSI device names are also referred to as SCSI stack addresses.

Example: 0:0:1:7

Related publication

  • Device Drivers, Features, and Commands, SC33-8411