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  • How to reattach a disk to XenServer

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It is easy to add new blank disk drives to XenServer and use them as new Storage Repositories (SR). See this article how to do that. Sometimes however it is required to add a disk drive and preserve the data on it:

  • a XenServer with one or more additional disk drives is reinstalled or upgraded.
  • a disk with a Storage Repository is moved to a different XenServer.

Reattach the disk drive to XenServer

Scenario: The disk drive /dev/sda contains a new XenServer installation, a second disk drive /dev/sdb from some other XenServer has been added to the server and contains a SR with some data, for example virtual machines or virtual disks.

The first step is to run the pvdisplay command. This will show what is available on the physical disks. We see that the second disk contains one physical LVM volume with 1.5 TByte of data.

No Format
[root@server15 ~]# pvdisplay
  --- Physical volume ---
  PV Name               /dev/sda3
  VG Name               VG_XenStorage-2a1d94fd-229b-29ea-0052-535698883e59
  PV Size               1.36 TB / not usable 7.25 MB
  Allocatable           yes
  PE Size (KByte)       4096
  Total PE              355648
  Free PE               353525
  Allocated PE          2123
  PV UUID               uRowsc-slAI-33dG-0Cln-UtQ9-d7eb-uTx6aI

  --- Physical volume ---
  PV Name               /dev/sdb1
  VG Name               VG_XenStorage-416a31b7-24a1-96b3-2984-901114b1155e
  PV Size               1.36 TB / not usable 7.25 MB
  Allocatable           yes
  PE Size (KByte)       4096
  Total PE              357696
  Free PE               357437
  Allocated PE          259
  PV UUID               YmRdHu-tAbB-zz0C-V20t-2AKN-fV5Z-rRkGNa

The VG name contains the uuid which we need for the xe sr-introduce command. This command will make the SR known to XenServer.

No Format
[root@server15 ~]# xe sr-introduce uuid=416a31b7-24a1-96b3-2984-901114b1155e type=lvm name-label="Local storage 2" content-type=user

The new SR will now show up in XenCenter but it is still marked as "Detached". We still have to connect the physical block device (PBD) with the SR. This is done by running the xe pbd-create command which needs the device name (so we run ls -l /dev/disk/by-id to find this out) and the host-uuid (we run xe host-list to get this). In this case, the partition on the physical block device we want to reconnect is /dev/sdb1. The corresponding disk id is scsi-SATA_SAMSUNG_HD154UIS24EJ9BZB02485-part1 which is used in the device-config parameter in the xe pbd-create command.

Finally, we need to activate the whole thing by executing xe pdb-plug.

No Format
[root@server15 ~]# ls -l /dev/disk/by-id
total 0
lrwxrwxrwx 1 root root  9 Sep  5 21:43 scsi-SATA_SAMSUNG_HD154UIS24EJ9BZB02485 -> ../../sdb
lrwxrwxrwx 1 root root 10 Sep  5 21:43 scsi-SATA_SAMSUNG_HD154UIS24EJ9BZB02485-part1 -> ../../sdb1
lrwxrwxrwx 1 root root  9 Sep  5 21:43 scsi-SATA_SAMSUNG_HD154UIS24EJ9BZB02486 -> ../../sda
lrwxrwxrwx 1 root root 10 Sep  5 21:43 scsi-SATA_SAMSUNG_HD154UIS24EJ9BZB02486-part1 -> ../../sda1
lrwxrwxrwx 1 root root 10 Sep  5 21:43 scsi-SATA_SAMSUNG_HD154UIS24EJ9BZB02486-part2 -> ../../sda2
lrwxrwxrwx 1 root root 10 Sep  5 21:43 scsi-SATA_SAMSUNG_HD154UIS24EJ9BZB02486-part3 -> ../../sda3

[root@server15 ~]# xe host-list
uuid ( RO)                : 767266f8-133e-4497-b332-72d495d33e8e
          name-label ( RW): server15
    name-description ( RW): Default install of XenServer

[root@server15 ~]# xe pbd-create host-uuid=767266f8-133e-4497-b332-72d495d33e8e sr-uuid=416a31b7-24a1-96b3-2984-901114b1155e \

[root@server15 ~]# xe pbd-plug uuid=ae239dca-4ed7-9a35-1d76-52f81bdcf65b

The SR should now be usable in XenCenter control panel. However, note that all names and descriptions of the partitions as well as their associations with virtual machines are unavailable, because this meta data is stored somewhere else.

Remove a disk from XenServer

To remove a disk from XenServer, we have to reverse the actions described above: disconnect the PBD from the SR using xe pdb-unplug, then forget about the SR using xe sr-forget. Use xe pbd-list and xe sr-list to find out the respective uuids.

No Format
[root@server15 ~]# xe pbd-list

uuid ( RO)                  : ae239dca-4ed7-9a35-1d76-52f81bdcf65b
             host-uuid ( RO): 767266f8-133e-4497-b332-72d495d33e8e
               sr-uuid ( RO): 416a31b7-24a1-96b3-2984-901114b1155e
         device-config (MRO): device: /dev/disk/by-id/scsi-SATA_SAMSUNG_HD154UIS24EJ9BZB02485-part1
    currently-attached ( RO): true

[root@server15 ~]# xe pbd-unplug uuid=ae239dca-4ed7-9a35-1d76-52f81bdcf65b

[root@server15 ~]# xe sr-list

uuid ( RO)                : 2a1d94fd-229b-29ea-0052-535698883e59
          name-label ( RW): Local storage
    name-description ( RW):
                host ( RO): server15
                type ( RO): lvm
        content-type ( RO): user

uuid ( RO)                : 416a31b7-24a1-96b3-2984-901114b1155e
          name-label ( RW): Local storage 2
    name-description ( RW):
                host ( RO): server15
                type ( RO): lvm
        content-type ( RO): user

[root@server15 ~]# xe sr-forget uuid=416a31b7-24a1-96b3-2984-901114b1155e