Howto resize XenServer LUN's Online

In the following procedure I will show how to extend iSCSI attached LUN's on XenServer (v 5.6 SP2 in my case) on the fly ,so no service restart or downtime are needed and the VDI's that reside on the resized LUN are not affected, read on!

First of all on the storage side (NetApp filer in my case)list the available LUN's, the LUN I want to resize is  called "my_lun30", with LUN ID of 22, which is currently allocated with 90GB.

For the test I will extend it by another 10GB, making it a 100GB LUN.

filer1> lun show
        /vol/vol1/my_lun10         300.0g (322163441664)  (r/w, online, mapped)
        /vol/vol2/my_lun20    200g (214748364800)  (r/w, online, mapped)
        /vol/vol2/my_lun30       90.0g (107388862464)  (r/w, online, mapped)


filer1> lun resize /vol/vol2/my_lun30 +10g
lun resize: resized to:  100.0g (107388862464)


As you can see, my_lun30 is now 100GB:

filer1> lun show
        /vol/vol1/my_lun10         300.0g (322163441664)  (r/w, online, mapped)
        /vol/vol2/my_lun20    200g (214748364800)  (r/w, online, mapped)
        /vol/vol2/my_lun30        100.0g (107388862464)  (r/w, online, mapped)

We are done with the storage side, let's head to the XenServer side.
 In case you work in pool mode, login to the pool master as root:

I suggest installing "lsscsi" which provides a nice way of viewing SCSI attached disks/LUNs:

[root@xen3]#yum install lsscsi -y

[root@xen3]# lsscsi
[0:0:0:0]    cd/dvd  Optiarc  DVD RW AD-7561S  AH52  /dev/scd0
[2:0:0:0]    disk    NETAPP   LUN              7340  /dev/sda
[2:0:0:22]   disk    NETAPP   LUN              7340  /dev/sdb
[2:0:0:33]   disk    NETAPP   LUN              7340  /dev/sdc
[3:0:0:1]    disk    NETAPP   LUN              7340  /dev/sdd
[3:0:0:3]    disk    NETAPP   LUN              7340  /dev/sde

If YUM traffic to a repository is blocked - It's also possible to see the SCSI id's under /proc via:

# cat /proc/scsi/scsi
Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
  Vendor: Optiarc  Model: DVD RW AD-7561S  Rev: AH52
  Type:   CD-ROM                           ANSI  SCSI revision: 05
Host: scsi2 Channel: 00 Id: 00 Lun: 00
  Vendor: NETAPP   Model: LUN              Rev: 7340
  Type:   Direct-Access                    ANSI  SCSI revision: 04
Host: scsi2 Channel: 00 Id: 00 Lun: 22
  Vendor: NETAPP   Model: LUN              Rev: 7340
  Type:   Direct-Access                    ANSI  SCSI revision: 04
Host: scsi2 Channel: 00 Id: 00 Lun: 33
  Vendor: NETAPP   Model: LUN              Rev: 7340
  Type:   Direct-Access                    ANSI  SCSI revision: 04
Host: scsi3 Channel: 00 Id: 00 Lun: 01
  Vendor: NETAPP   Model: LUN              Rev: 7340
  Type:   Direct-Access                    ANSI  SCSI revision: 04
Host: scsi3 Channel: 00 Id: 00 Lun: 03
  Vendor: NETAPP   Model: LUN              Rev: 7340
  Type:   Direct-Access                    ANSI  SCSI revision: 04

From the output we can see the SCSI ID of the LUN + it's corresponding device on the system, and check the device physical size, as you can see it is not updated yet:

[root@xen3 backup_scripts]# fdisk -l /dev/sdb

Disk /dev/sdb: 96.6 GB, 96647249920 bytes
255 heads, 63 sectors/track, 11750 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/sdb doesn't contain a valid partition table

Since XenServer uses LVM, we can see the physical volume info of the disk, as you can see the size is still 90GB.
  
[root@xen3]# pvdisplay /dev/sdb
  --- Physical volume ---
  PV Name               /dev/sdb
  VG Name               VG_XenStorage-e71389d1-4dc3-2518-aa30-9f5f0c70ba12
  PV Size               90.01 GB / not usable 6.12 MB
  Allocatable           yes
  PE Size (KByte)       4096
  Total PE              23039
  Free PE               16624
  Allocated PE          6415
  PV UUID               oSZlnA-VxlA-3qbp-07nI-Ql0b-3cG2-9wo2lC


Now, we will tell XenServer to rescan the SCSI bus, we will provide the SCSI id which we previously got from the "lsscsi" command (2:0:0:22):

[root@xen3]# echo 1 > /sys/class/scsi_disk/2:0:0:22/device/rescan

You can notice the immediate change of /dev/sdb:

[root@xen3]# fdisk -l /dev/sdb

Disk /dev/sdb: 107.3 GB, 107388862464 bytes
255 heads, 63 sectors/track, 13055 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/sdb doesn't contain a valid partition table

Now, resize the physical volume with:

[root@xen3]# pvresize /dev/sdb

  Physical volume "/dev/sdb" changed
  1 physical volume(s) resized / 0 physical volume(s) not resized

Check again the physical volume size, notice the change:

[root@xen3]#  pvdisplay /dev/sdb
  --- Physical volume ---
  PV Name               /dev/sdb
  VG Name               VG_XenStorage-e71389d1-4dc3-2518-aa30-9f5f0c70ba12
  PV Size               100.01 GB / not usable 6.12 MB
  Allocatable           yes
  PE Size (KByte)       4096
  Total PE              25600
  Free PE               19185
  Allocated PE          6415
  PV UUID               oSZlnA-VxlA-3qbp-07nI-Ql0b-3cG2-9wo2lC

Let's get the SR uuid, I know the LUN ID is 22, so:

[root@xen3]# xe sr-list|grep lun22 -B1
uuid ( RO)                : e71389d1-4dc3-2518-aa30-9f5f0c70ba12
          name-label ( RW): iSCSI_filer1_lun22

Notice that the SR size has yet to be updated:

[root@xen3]#  xe sr-param-list uuid=e71389d1-4dc3-2518-aa30-9f5f0c70ba12|grep physical-size
           physical-size ( RO): 96632569856

Now, finally update the relevant SR:

[root@xen3]#  xe sr-update uuid=e71389d1-4dc3-2518-aa30-9f5f0c70ba12

And at last, the SR is updated with the correct new LUN size :

[root@xen3]#  xe sr-param-list uuid=e71389d1-4dc3-2518-aa30-9f5f0c70ba12|grep physical-size
           physical-size ( RO): 107374182400


You are done!