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    Thursday, July 24, 2014

    How to detect new hard disk attached without rebooting in Linux

    Scenario:

    Suppose you have added a new hard disk to your Linux OS running on any Virtual Environment which in my case is VMware workstation. Once added the new hard drive, generally the changes won't reflect unless you reboot the Guest OS.

    But what if you are in no position to reboot the Gues Linux OS?

    Solution:

    In the below path you can find a list of host symlinks pointing to the iscsi device configured on your Linux box
    # ls -l /sys/class/scsi_host/
    total 0
    lrwxrwxrwx 1 root root 0 Jun 14 05:08 host0 -> ../../devices/pci0000:00/0000:00:07.1/host0/scsi_host/host0
    lrwxrwxrwx 1 root root 0 Jun 14 05:08 host1 -> ../../devices/pci0000:00/0000:00:07.1/host1/scsi_host/host1
    lrwxrwxrwx 1 root root 0 Jun 14 05:08 host10 -> ../../devices/pci0000:00/0000:00:11.0/0000:02:05.0/host10/scsi_host/host10
    lrwxrwxrwx 1 root root 0 Jun 14 05:08 host2 -> ../../devices/pci0000:00/0000:00:10.0/host2/scsi_host/host2
    lrwxrwxrwx 1 root root 0 Jun 14 05:08 host3 -> ../../devices/pci0000:00/0000:00:11.0/0000:02:05.0/host3/scsi_host/host3
    lrwxrwxrwx 1 root root 0 Jun 14 05:08 host4 -> ../../devices/pci0000:00/0000:00:11.0/0000:02:05.0/host4/scsi_host/host4
    lrwxrwxrwx 1 root root 0 Jun 14 05:08 host5 -> ../../devices/pci0000:00/0000:00:11.0/0000:02:05.0/host5/scsi_host/host5
    lrwxrwxrwx 1 root root 0 Jun 14 05:08 host6 -> ../../devices/pci0000:00/0000:00:11.0/0000:02:05.0/host6/scsi_host/host6
    lrwxrwxrwx 1 root root 0 Jun 14 05:08 host7 -> ../../devices/pci0000:00/0000:00:11.0/0000:02:05.0/host7/scsi_host/host7
    lrwxrwxrwx 1 root root 0 Jun 14 05:08 host8 -> ../../devices/pci0000:00/0000:00:11.0/0000:02:05.0/host8/scsi_host/host8
    lrwxrwxrwx 1 root root 0 Jun 14 05:08 host9 -> ../../devices/pci0000:00/0000:00:11.0/0000:02:05.0/host9/scsi_host/host9

    But to detect a new hard drive attached you need to first get your host bus number used which you can get by using below command
    # grep mpt /sys/class/scsi_host/host?/proc_name
    You should get a output like below
    /sys/class/scsi_host/host2/proc_name:mptspi
    So as you see your host2 is the relevant fiels where you need to reset the storage buffer values. Run the below command
    # echo "- - -" > /sys/class/scsi_host/host2/scan
    Here "- - -" defines the three values stored inside host*/scan i.e. channel number, SCSI target ID, and LUN values. We are simply replacing the values with wild cards so that it can detect new changes attached to the Linux box. This procedure will add LUNs, but not remove them.

    Once done verify if you can see the new hard drive which in my case worked very fine as I see below
    # fdisk -l
    Disk
    /dev/sdb: 3221 MB, 3221225472 bytes
    255 heads, 63 sectors/track, 391 cylinders
    Units = cylinders of 16065 * 512 = 8225280 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disk identifier: 0x00000000

    Let me know your success and failures.

    Related Articles:
    How to extend/resize Logical Volume and Volume Group in Linux
    How to detect new NIC/Ethernet card without rebooting in Linux
    How do you check Linux machine is Physical or Virtual remotely?


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    9 comments:

    1. Hello Prasad,

      Quick tip:
      A better way to identify new disks is using the rescan-scsi-bus.sh script.
      You can install it with by 'yum install sg3_utils'.

      Some options you'll want to use are: -c or -cr.

      By the way, your 'Configure Red Hat Cluster using VMware, Quorum Disk, GFS2, Openfiler' is really good. Congrats and keep the good tutorials.

      ReplyDelete
    2. great, it was what i was looking for

      work on sles 11 sp3. ( over vmware)

      in messages log you can see the adition.


      ReplyDelete
    3. We can also check the newly added disks using dmesg command

      ReplyDelete
    4. Hi,

      This article is very nice, it helped me a lot.

      Keep posting this kind useful information.

      Thanks a lot

      ReplyDelete
    5. what is kernel patching
      how to upgrade kerner patching
      send me answer in brief please

      ReplyDelete