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thepearson
Asked: 2011-09-01 14:21:09 +0800 CST

Centos Xen resizing DomU partition and volume group

  • 772

I have a setup like so:

      Dom0 LV
         |
 DomU Physical Disk
    |           |
  XVDA1       XVDA2
 (/boot)    (DomU PV)
                |
            VolGroup00
            (DomU VG)
            |        |
      LogVol00       LogVol01
       (swap)         (/)

I am trying to resize the DomU root Filesystem. (VolGroup00-LogVol01) I realize that I now need to resize the partition XVDA2, however when I try doing this with parted on Dom0 it just tells me "Error: Could not detect file system."

So to resize the root part VolGroup-LogVol00 shouldn't the process be:

# Shut down DomU
xm shutdown domU

#Resize Dom0 Logical volume
lvextend -L+2G /dev/volumes/domU-vol

# Parted 
parted /dev/volumes/domU-vol

# Resize root partition
resize 2 START END

(This is where I get an error) "Error: Could not detect file system."


# add the vm volume group to Dom0 lvm
kpartx -a /dev/volumes/domU-vol

# resize the domU PV
pvresize /dev/mapper/domU-pl (as listed in pvdisplay)

# The domU volume group should automatically adjust
# resize the DomU lv
lvextend -L+2G /dev/VolGroup/LogVol00

And then obviously increase the fs, remove the device from kpartx etc

The problem is I dont know how to resize the partition? How do I resize this partition so I can run pvresize on the DomU?

Thanks

xen centos lvm

3 Answers

  1. Here are the steps that I roughly followed to resize a KVM guest that used LVM internally.

    1. Shutdown the VM
    2. add more space to the guest's "image file" (something like: cat old.img 10G_addon.raw >> new.img
    3. start the VM (using the newly created new.img)

    4. run fdisk inside VM and delete & re-create LVM partition

      % fdisk /dev/vda
...
Device Boot      Start         End      Blocks   Id  System
/dev/vda1   *           1          13      104391   83  Linux
/dev/vda2              14        3263    26105625   8e  Linux LVM

Command (m for help): d
Partition number (1-4): 2

Command (m for help): p

Disk /dev/vda: 48.3 GB, 48318382080 bytes
255 heads, 63 sectors/track, 5874 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot      Start         End      Blocks   Id  System
/dev/vda1   *           1          13      104391   83  Linux

Command (m for help): n 
Command action
  e   extended
  p   primary partition (1-4)
p
Partition number (1-4): 2
First cylinder (14-5874, default 14): 14
Last cylinder or +size or +sizeM or +sizeK (14-5874, default 5874): 
Using default value 5874

Command (m for help): p

Disk /dev/vda: 48.3 GB, 48318382080 bytes
255 heads, 63 sectors/track, 5874 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot      Start         End      Blocks   Id  System
/dev/vda1   *           1          13      104391   83  Linux
/dev/vda2              14        5874    47078482+  83  Linux

Command (m for help): t
Partition number (1-4): 2
Hex code (type L to list codes): 8e
Changed system type of partition 2 to 8e (Linux LVM)

Command (m for help): p

Disk /dev/vda: 48.3 GB, 48318382080 bytes
255 heads, 63 sectors/track, 5874 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot      Start         End      Blocks   Id  System
/dev/vda1   *           1          13      104391   83  Linux
/dev/vda2              14        5874    47078482+  8e  Linux LVM

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: Device or 
resource busy.
The kernel still uses the old table.
The new table will be used at the next reboot.
Syncing disks.
%

    5. Reboot the VM

    6. Resize the LVM physical volume

      % pvdisplay 
  --- Physical volume ---
  PV Name               /dev/vda2
  VG Name               VolGroup00
  PV Size               24.90 GB / not usable 21.59 MB
  Allocatable           yes (but full)
  PE Size (KByte)       32768
  Total PE              796
  Free PE               0
  ...

% pvresize /dev/vda2

% pvdisplay
  --- Physical volume ---
  PV Name               /dev/vda2
  VG Name               VolGroup00
  PV Size               44.90 GB / not usable 22.89 MB
  Allocatable           yes 
  PE Size (KByte)       32768
  Total PE              1436
  Free PE               640
  ...

    7. Resize the LVM Logical Volume

        % lvresize /dev/VolGroup00/LogVol00 -l +640
  Extending logical volume LogVol00 to 43.88 GB
  Logical volume LogVol00 successfully resized

    8. Grow the File system

        % resize2fs /dev/VolGroup00/LogVol00 
  resize2fs 1.39 (29-May-2006)
  Filesystem at /dev/VolGroup00/LogVol00 is mounted on /; on-line resizing required
  Performing an on-line resize of /dev/VolGroup00/LogVol00 to 11501568 (4k) blocks.
  The filesystem on /dev/VolGroup00/LogVol00 is now 11501568 blocks long.

    The above is my example, but I followed the steps on this website

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  2. So, to clarify: you need to resize the root LV inside the VM, but the VG is full so you first need to resize the physical partition the PV lives on? Assuming that is correct, we continue...

    I'm surprised that parted would have such a hissy-fit over the dom0 partition. From it's point of view, it's just an in-use LVM PV. I've never been particularly impressed with parted, though, and I just stick with good ol' fdisk.

    You'll probably have trouble resizing the partition while the disk is in use, anyway, because rescanning the partition table on a mounted filesystem is... tricky. It'd be best to shutdown the VM and do all the operations from the dom0.

    I'd recommend skipping partitions entirely and doing everything with LVM; I also don't like LVM in my VMs because they've got poor enough I/O throughput as it is. Just attach a bunch of LVs from the dom0 for the partitions in the VMs -- this also makes replication easier, as you don't typically want to replicate swap (unless you're doing live migration, but then it's just one more block device to replicate anyway).

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  3. Also be very careful when resizing.

    It seems the step you are having trouble with is the parted step:

    http://www.gnu.org/software/parted/manual/html_chapter/parted_7.html#SEC68

    Be careful to follow the note and you may also want to use fdisk -l on the partition to make sure it is the partition type and file system that you expect.

    Other good general references that could provide you or others help: http://linuxwave.blogspot.com/2008/08/resizing-your-xen-domu-using-lvm.html

    http://www.novell.com/communities/node/4790/how-resize-xen-file-based-disk-vms-ext3-or-reiser-sles-10-sp1

    http://webcache.googleusercontent.com/search?q=cache:jNh6rSBUqVEJ:grantmcwilliams.com/tech/virtualization/xen-howtos/265-resize-xen-disk-image-used-as-domu-partition+grant+mcwilliams+xen+resize+howto&cd=4&hl=en&ct=clnk&gl=us

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