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virt-resize

Langue: en

Version: 2010-09-27 (fedora - 01/12/10)

Section: 1 (Commandes utilisateur)

NAME

virt-resize - Resize a virtual machine disk

SYNOPSIS

  virt-resize [--resize /dev/sdaN=[+/-]<size>[%]]
    [--expand /dev/sdaN] [--shrink /dev/sdaN]
    [--ignore /dev/sdaN] [--delete /dev/sdaN] [...] indisk outdisk
 
 

DESCRIPTION

Virt-resize is a tool which can resize a virtual machine disk, making it larger or smaller overall, and resizing or deleting any partitions contained within.

Virt-resize cannot resize disk images in-place. Virt-resize should not be used on live virtual machines - for consistent results, shut the virtual machine down before resizing it.

If you are not familiar with the associated tools: virt-list-partitions(1), virt-list-filesystems(1) and virt-df(1), we recommend you go and read those manual pages first.

EXAMPLES

Copy "olddisk" to "newdisk", extending one of the guest's partitions to fill the extra 5GB of space.
  truncate -r olddisk newdisk; truncate -s +5G newdisk
  virt-list-partitions -lht olddisk
  # Note "/dev/sda2" is a partition inside the "olddisk" file.
  virt-resize --expand /dev/sda2 olddisk newdisk
 
 

As above, but make the /boot partition 200MB bigger, while giving the remaining space to /dev/sda2:

  virt-resize --resize /dev/sda1=+200M --expand /dev/sda2 olddisk newdisk
 
 

DETAILED USAGE

EXPANDING A VIRTUAL MACHINE DISK

1. Shut down the virtual machine
2. Locate input disk image
Locate the input disk image (ie. the file or device on the host containing the guest's disk). If the guest is managed by libvirt, you can use "virsh dumpxml" like this to find the disk image name:
  # virsh dumpxml guestname | xpath /domain/devices/disk/source
  Found 1 nodes:
  -- NODE --
  <source dev="/dev/vg/lv_guest" />
 
 
3. Look at current sizing
Use virt-list-partitions(1) to display the current partitions and sizes:
  # virt-list-partitions -lht /dev/vg/lv_guest
  /dev/sda1 ext3 101.9M
  /dev/sda2 pv 7.9G
  /dev/sda device 8.0G
 
 

(This example is a virtual machine with an 8 GB disk which we would like to expand up to 10 GB).

4. Create output disk
Virt-resize cannot do in-place disk modifications. You have to have space to store the resized output disk.

To store the resized disk image in a file, create a file of a suitable size:

  # rm -f outdisk
  # truncate -s 10G outdisk
 
 

Or use lvcreate(1) to create a logical volume:

  # lvcreate -L 10G -n lv_name vg_name
 
 

Or use virsh(1) vol-create-as to create a libvirt storage volume:

  # virsh pool-list
  # virsh vol-create-as poolname newvol 10G
 
 
5. Resize
virt-resize takes two mandatory parameters, the input disk (eg. device or file) and the output disk. The output disk is the one created in the previous step.
  # virt-resize indisk outdisk
 
 

This command just copies disk image "indisk" to disk image "outdisk" without resizing or changing any existing partitions. If "outdisk" is larger, then an extra, empty partition is created at the end of the disk covering the extra space. If "outdisk" is smaller, then it will give an error.

More realistically you'd want to expand existing partitions in the disk image by passing extra options (for the full list see the ``OPTIONS'' section below).

``--expand'' is the most useful option. It expands the named partition within the disk to fill any extra space:

  # virt-resize --expand /dev/sda2 indisk outdisk
 
 

(In this case, an extra partition is not created at the end of the disk, because there will be no unused space).

``--resize'' is the other commonly used option. The following would increase the size of /dev/sda1 by 200M, and expand /dev/sda2 to fill the rest of the available space:

  # virt-resize --resize /dev/sda1=+200M --expand /dev/sda2 \
      indisk outdisk
 
 

If the expanded partition in the image contains a filesystem or LVM PV, then if virt-resize knows how, it will resize the contents, the equivalent of calling a command such as pvresize(8), resize2fs(8) or ntfsresize(8). However virt-resize does not know how to resize some filesystems, so you would have to online resize them after booting the guest. And virt-resize also does not resize anything inside an LVM PV, it just resizes the PV itself and leaves the user to resize any LVs inside that PV as desired.

Other options are covered below.

6. Test
Thoroughly test the new disk image before discarding the old one.

If you are using libvirt, edit the XML to point at the new disk:

  # virsh edit guestname
 
 

Change <source ...>, see <http://libvirt.org/formatdomain.html#elementsDisks>

Then start up the domain with the new, resized disk:

  # virsh start guestname
 
 

and check that it still works. See also the ``NOTES'' section below for additional information.

7. Resize LVs etc inside the guest
(This can also be done offline using guestfish(1))

Once the guest has booted you should see the new space available, at least for filesystems that virt-resize knows how to resize, and for PVs. The user may need to resize LVs inside PVs, and also resize filesystem types that virt-resize does not know how to expand.

SHRINKING A VIRTUAL MACHINE DISK

Shrinking is somewhat more complex than expanding, and only an overview is given here.

Firstly virt-resize will not attempt to shrink any partition content (PVs, filesystems). The user has to shrink content before passing the disk image to virt-resize, and virt-resize will check that the content has been shrunk properly.

(Shrinking can also be done offline using guestfish(1))

After shrinking PVs and filesystems, shut down the guest, and proceed with steps 3 and 4 above to allocate a new disk image.

Then run virt-resize with any of the "--shrink" and/or "--resize" options.

IGNORING OR DELETING PARTITIONS

virt-resize also gives a convenient way to ignore or delete partitions when copying from the input disk to the output disk. Ignoring a partition speeds up the copy where you don't care about the existing contents of a partition. Deleting a partition removes it completely, but note that it also renumbers any partitions after the one which is deleted, which can leave some guests unbootable.

OPTIONS

--help
Display help.
--version
Display version number and exit.
--resize part=size
Resize the named partition (expanding or shrinking it) so that it has the given size.

"size" can be expressed as an absolute number followed by b/K/M/G/T/P/E to mean bytes, Kilobytes, Megabytes, Gigabytes, Terabytes, Petabytes or Exabytes; or as a percentage of the current size; or as a relative number or percentage. For example:

  --resize /dev/sda2=10G
 
  --resize /dev/sda4=90%
 
  --resize /dev/sda2=+1G
 
  --resize /dev/sda2=-200M
 
  --resize /dev/sda1=+128K
 
  --resize /dev/sda1=+10%
 
  --resize /dev/sda1=-10%
 
 

You can increase the size of any partition. Virt-resize will expand the direct content of the partition if it knows how (see "--expand" below).

You can only decrease the size of partitions that contain filesystems or PVs which have already been shrunk. Virt-resize will check this has been done before proceeding, or else will print an error (see also "--resize-force").

You can give this option multiple times.

--resize-force part=size
This is the same as "--resize" except that it will let you decrease the size of any partition. Generally this means you will lose any data which was at the end of the partition you shrink, but you may not care about that (eg. if shrinking an unused partition, or if you can easily recreate it such as a swap partition).

See also the "--ignore" option.

--expand part
Expand the named partition so it uses up all extra space (space left over after any other resize changes that you request have been done).

If virt-resize knows how, it will expand the direct content of the partition. For example, if the partition is an LVM PV, it will expand the PV to fit (like calling pvresize(8)). Virt-resize leaves any other content it doesn't know about alone.

Currently virt-resize can resize:

*
ext2, ext3 and ext4 filesystems when they are contained directly inside a partition.
*
NTFS filesystems contained directly in a partition, if libguestfs was compiled with support for NTFS.

The filesystem must have been shut down consistently last time it was used. Additionally, ntfsresize(8) marks the resized filesystem as requiring a consistency check, so at the first boot after resizing Windows will check the disk.

*
LVM PVs (physical volumes). However virt-resize does not resize anything inside the PV. The user will have to resize LVs as desired.

Note that you cannot use "--expand" and "--shrink" together.
--shrink part
Shrink the named partition until the overall disk image fits in the destination. The named partition must contain a filesystem or PV which has already been shrunk using another tool (eg. guestfish(1) or other online tools). Virt-resize will check this and give an error if it has not been done.

The amount by which the overall disk must be shrunk (after carrying out all other operations requested by the user) is called the ``deficit''. For example, a straight copy (assume no other operations) from a 5GB disk image to a 4GB disk image results in a 1GB deficit. In this case, virt-resize would give an error unless the user specified a partition to shrink and that partition had more than a gigabyte of free space.

Note that you cannot use "--expand" and "--shrink" together.

--ignore part
Ignore the named partition. Effectively this means the partition is allocated on the destination disk, but the content is not copied across from the source disk. The content of the partition will be blank (all zero bytes).

You can give this option multiple times.

--delete part
Delete the named partition. It would be more accurate to describe this as ``don't copy it over'', since virt-resize doesn't do in-place changes and the original disk image is left intact.

Note that when you delete a partition, then anything contained in the partition is also deleted. Furthermore, this causes any partitions that come after to be renumbered, which can easily make your guest unbootable.

You can give this option multiple times.

--LV-expand logvol
This takes the logical volume and, as a final step, expands it to fill all the space available in its volume group. A typical usage, assuming a Linux guest with a single PV "/dev/sda2" and a root device called "/dev/vg_guest/lv_root" would be:
  virt-resize indisk outdisk \
    --expand /dev/sda2 --LV-expand /dev/vg_guest/lv_root
 
 

This would first expand the partition (and PV), and then expand the root device to fill the extra space in the PV.

The contents of the LV are also resized if virt-resize knows how to do that. You can stop virt-resize from trying to expand the content by using the option "--no-expand-content".

Use virt-list-filesystems(1) to list the filesystems in the guest.

You can give this option multiple times, but it doesn't make sense to do this unless the logical volumes you specify are all in different volume groups.

--no-copy-boot-loader
By default, virt-resize copies over some sectors at the start of the disk (up to the beginning of the first partition). Commonly these sectors contain the Master Boot Record (MBR) and the boot loader, and are required in order for the guest to boot correctly.

If you specify this flag, then this initial copy is not done. You may need to reinstall the boot loader in this case.

--no-extra-partition
By default, virt-resize creates an extra partition if there is any extra, unused space after all resizing has happened. Use this option to prevent the extra partition from being created. If you do this then the extra space will be inaccessible until you run fdisk, parted, or some other partitioning tool in the guest.

Note that if the surplus space is smaller than 10 MB, no extra partition will be created.

--no-expand-content
By default, virt-resize will try to expand the direct contents of partitions, if it knows how (see "--expand" option above).

If you give the "--no-expand-content" option then virt-resize will not attempt this.

-d | --debug
Enable debugging messages.
-n | --dryrun
Print a summary of what would be done, but don't do anything.
-q | --quiet
Don't print the summary.

NOTES

Partition 1 does not end on cylinder boundary.

Virt-resize aligns partitions to multiples of 64 sectors. Usually this means the partitions will not be aligned to the ancient CHS geometry. However CHS geometry is meaningless for disks manufactured since the early 1990s, and doubly so for virtual hard drives. Alignment of partitions to cylinders is not required by any modern operating system.

RESIZING WINDOWS VIRTUAL MACHINES

In Windows Vista and later versions, Microsoft switched to using a separate boot partition. In these VMs, typically "/dev/sda1" is the boot partition and "/dev/sda2" is the main (C:) drive. We have not had any luck resizing the boot partition. Doing so seems to break the guest completely. However expanding the second partition (ie. C: drive) should work.

Windows may initiate a lengthy ``chkdsk'' on first boot after a resize, if NTFS partitions have been expanded. This is just a safety check and (unless it find errors) is nothing to worry about.

ALTERNATIVE TOOLS

There are several proprietary tools for resizing partitions. We won't mention any here.

parted(8) and its graphical shell gparted can do some types of resizing operations on disk images. They can resize and move partitions, but I don't think they can do anything with the contents, and they certainly don't understand LVM.

guestfish(1) can do everything that virt-resize can do and a lot more, but at a much lower level. You will probably end up hand-calculating sector offsets, which is something that virt-resize was designed to avoid. If you want to see the guestfish-equivalent commands that virt-resize runs, use the "--debug" flag.

SEE ALSO

virt-list-partitions(1), virt-list-filesystems(1), virt-df(1), guestfs(3), guestfish(1), lvm(8), pvresize(8), lvresize(8), resize2fs(8), ntfsresize(8), virsh(1), parted(8), Sys::Guestfs(3), <http://libguestfs.org/>.

AUTHOR

Richard W.M. Jones <http://people.redhat.com/~rjones/> Copyright (C) 2010 Red Hat Inc.

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

DIPLÔMES

P : Sans le bac, tu peux faire chien de garde...
M : C'est nul...
P : Ça, c'est sûr ! Mais il y a pire... Dis-toi que si tu n'avais pas le brevet, tu ne pourrais faire que maître chien...