Topic
  • 4 replies
  • Latest Post - ‏2009-09-18T00:12:22Z by SystemAdmin
SystemAdmin
SystemAdmin
706 Posts

Pinned topic query on device detection

‏2009-09-15T02:20:47Z |
Hi,
I'm new in Power Linux and have a question about how Linux detects devices.
From the Link below, I've learned that you need to rescan the SCSI bus to add/remove SCSI devices without reboot(like the "cfgmgr" command in AIX)
http://kbase.redhat.com/faq/docs/DOC-3942

However, what I used to believed was that Linux can automatically create devices by the udev daemon. I've already seen my ubuntu machine automatically add files to /dev when I plugged in my usb HDD.

Can Anyone explain why the udev daemon cannot create scsi devices & also is there any other devices that the udev daemon cannot create

Thanks
Updated on 2009-09-18T00:12:22Z at 2009-09-18T00:12:22Z by SystemAdmin
  • Brian_King
    Brian_King
    20 Posts

    Re: query on device detection

    ‏2009-09-15T13:20:28Z  
    It depends on the transport and the SCSI adapter driver. Transports that are hot plug transports, such as USB, SAS, and Fibre Channel, typically do not need to have their SCSI bus manually rescanned. Non hot plug transports, such as parallel SCSI (SPI), typically do need to have their SCSI bus rescanned to detect new devices. On Power, however, the vast majority of SCSI adapters are from the IPR family of adapters (controlled by the ipr adapter device driver). On these adapters, even for non-hotplug transports such as parallel SCSI, the adapter firmware regularly polls the SCSI bus for new devices and will report these new devices to the driver so they will automatically show up.
  • SystemAdmin
    SystemAdmin
    706 Posts

    Re: query on device detection

    ‏2009-09-16T00:27:04Z  
    It depends on the transport and the SCSI adapter driver. Transports that are hot plug transports, such as USB, SAS, and Fibre Channel, typically do not need to have their SCSI bus manually rescanned. Non hot plug transports, such as parallel SCSI (SPI), typically do need to have their SCSI bus rescanned to detect new devices. On Power, however, the vast majority of SCSI adapters are from the IPR family of adapters (controlled by the ipr adapter device driver). On these adapters, even for non-hotplug transports such as parallel SCSI, the adapter firmware regularly polls the SCSI bus for new devices and will report these new devices to the driver so they will automatically show up.
    Thanks for the reply! Your answer was very helpful.
    let me confirm one thing.

    First of all, I asked this question because I was struggling how to add LUNs to my Linux machine (RedHat 5.3) without reboots. The LUNs are provided through 2 VIOS's(2.1.1.10-FP21) and dm-mp as the multipath driver. The LUNs finally appeared after rescanning the SCSI bus.

    From the answer above does this mean that

    ・Virtual SCSI adapters, does not poll for new devices. So when adding Virtual SCSI devices (like virtual disks and virtual optical devices) it is required to rescan the SCSI bus.

    Thanks,
  • Brian_King
    Brian_King
    20 Posts

    Re: query on device detection

    ‏2009-09-16T14:04:09Z  
    Thanks for the reply! Your answer was very helpful.
    let me confirm one thing.

    First of all, I asked this question because I was struggling how to add LUNs to my Linux machine (RedHat 5.3) without reboots. The LUNs are provided through 2 VIOS's(2.1.1.10-FP21) and dm-mp as the multipath driver. The LUNs finally appeared after rescanning the SCSI bus.

    From the answer above does this mean that

    ・Virtual SCSI adapters, does not poll for new devices. So when adding Virtual SCSI devices (like virtual disks and virtual optical devices) it is required to rescan the SCSI bus.

    Thanks,
    That is correct. Virtual SCSI does not poll for new devices. When adding Virtual SCSI devices you need to manually rescan the SCSI bus.
  • SystemAdmin
    SystemAdmin
    706 Posts

    Re: query on device detection

    ‏2009-09-18T00:12:22Z  
    That is correct. Virtual SCSI does not poll for new devices. When adding Virtual SCSI devices you need to manually rescan the SCSI bus.
    Thanks!