path: root/sparsify/virt-sparsify.pod

=encoding utf8

=head1 NAME

virt-sparsify - Make a virtual machine disk sparse

=head1 SYNOPSIS

 virt-sparsify [--options] indisk outdisk

=head1 DESCRIPTION

Virt-sparsify is a tool which can make a virtual machine disk (or any
disk image) sparse a.k.a. thin-provisioned.  This means that free
space within the disk image can be converted back to free space on the
host.

Virt-sparsify can locate and sparsify free space in most filesystems
(eg. ext2/3/4, btrfs, NTFS, etc.), and also in LVM physical volumes.

Virt-sparsify can also convert between some disk formats, for example
converting a raw disk image to a thin-provisioned qcow2 image.

Virt-sparsify can operate on any disk image, not just ones from
virtual machines.  If a virtual machine has more than one attached
disk, you must sparsify each one separately.

=head2 IMPORTANT NOTE ABOUT SPARSE OUTPUT IMAGES

If the input is raw, then the default output is raw sparse.  B<You
must check the output size using a tool that understands sparseness>
such as C<du -sh>.  It can make a huge difference:

 $ ls -lh test1.img
 -rw-rw-r--. 1 rjones rjones 100M Aug  8 08:08 test1.img
 $ du -sh test1.img
 3.6M	test1.img

(Compare the apparent size B<100M> vs the actual size B<3.6M>)

=head2 IMPORTANT LIMITATIONS

=over 4

=item *

Virt-sparsify does not do in-place modifications.  It copies from a
source image to a destination image, leaving the source unchanged.
I<Check that the sparsification was successful before deleting the
source image>.

=item *

The virtual machine I<must be shut down> before using this tool.

=item *

Virt-sparsify may require up to 2x the virtual size of the source disk
image (1 temporary copy + 1 destination image).  This is in the worst
case and usually much less space is required.

=item *

Virt-sparsify cannot resize disk images.  To do that, use
L<virt-resize(1)>.

=item *

Virt-sparsify cannot handle encrypted disks.  Libguestfs supports
encrypted disks, but encrypted disks themselves cannot be sparsified.

=item *

Virt-sparsify cannot yet sparsify the space between partitions.  Note
that this space is often used for critical items like bootloaders so
it's not really unused.

=back

You may also want to read the manual pages for the associated tools
L<virt-filesystems(1)> and L<virt-df(1)> before starting.

=head1 EXAMPLES

Typical usage is:

 virt-sparsify indisk outdisk

which copies C<indisk> to C<outdisk>, making the output sparse.
C<outdisk> is created, or overwritten if it already exists.  The
format of the input disk is detected (eg. qcow2) and the same format
is used for the output disk.

To convert between formats, use the I<--convert> option:

 virt-sparsify disk.raw --convert qcow2 disk.qcow2

Virt-sparsify tries to zero and sparsify free space on every
filesystem it can find within the source disk image.  You can get it
to ignore (don't zero free space on) certain filesystems by doing:

 virt-sparsify --ignore /dev/sda1 indisk outdisk

See L<virt-filesystems(1)> to get a list of filesystems within a disk
image.

=head1 OPTIONS

=over 4

=item B<--help>

Display help.

=item B<--compress>

Compress the output file.  This I<only> works if the output format is
C<qcow2>.

=item B<--convert> raw

=item B<--convert> qcow2

=item B<--convert> [other formats]

Use C<output-format> as the format for the destination image.  If this
is not specified, then the input format is used.

Supported and known-working output formats are: C<raw>, C<qcow2>, C<vdi>.

You can also use any format supported by the L<qemu-img(1)> program,
eg. C<vmdk>, but support for other formats is reliant on qemu.

Specifying the I<--convert> option is usually a good idea, because
then virt-sparsify doesn't need to try to guess the input format.

For fine-tuning the output format, see: I<--compress>, I<-o>.

=item B<--debug-gc>

Debug garbage collection and memory allocation.  This is only useful
when debugging memory problems in virt-sparsify or the OCaml libguestfs
bindings.

=item B<--format> raw

=item B<--format> qcow2

Specify the format of the input disk image.  If this flag is not
given then it is auto-detected from the image itself.

If working with untrusted raw-format guest disk images, you should
ensure the format is always specified.

=item B<--ignore> filesystem

=item B<--ignore> volgroup

Ignore the named filesystem.  Free space on the filesystem will not be
zeroed, but existing blocks of zeroes will still be sparsified.

In the second form, this ignores the named volume group.  Use the
volume group name without the C</dev/> prefix, eg. I<--ignore vg_foo>

You can give this option multiple times.

=item B<--machine-readable>

This option is used to make the output more machine friendly
when being parsed by other programs.  See
L</MACHINE READABLE OUTPUT> below.

=item B<-o> option[,option,...]

Pass I<-o> option(s) to the L<qemu-img(1)> command to fine-tune the
output format.  Options available depend on the output format (see
I<--convert>) and the installed version of the qemu-img program.

You should use I<-o> at most once.  To pass multiple options, separate
them with commas, eg:

 virt-sparsify --convert qcow2 \
   -o cluster_size=512,preallocation=metadata ...

=item B<-q>

=item B<--quiet>

This disables progress bars and other unnecessary output.

=item B<-v>

=item B<--verbose>

Enable verbose messages for debugging.

=item B<-V>

=item B<--version>

Display version number and exit.

=item B<-x>

Enable tracing of libguestfs API calls.

=item B<--zero> partition

=item B<--zero> logvol

Zero the contents of the named partition or logical volume in the
guest.  All data on the device is lost, but sparsification is
excellent!  You can give this option multiple times.

=back

=head1 MACHINE READABLE OUTPUT

The I<--machine-readable> option can be used to make the output more
machine friendly, which is useful when calling virt-sparsify from
other programs, GUIs etc.

There are two ways to use this option.

Firstly use the option on its own to query the capabilities of the
virt-sparsify binary.  Typical output looks like this:

 $ virt-sparsify --machine-readable
 virt-sparsify
 ntfs
 btrfs

A list of features is printed, one per line, and the program exits
with status 0.

Secondly use the option in conjunction with other options to make the
regular program output more machine friendly.

At the moment this means:

=over 4

=item 1.

Progress bar messages can be parsed from stdout by looking for this
regular expression:

 ^[0-9]+/[0-9]+$

=item 2.

The calling program should treat messages sent to stdout (except for
progress bar messages) as status messages.  They can be logged and/or
displayed to the user.

=item 3.

The calling program should treat messages sent to stderr as error
messages.  In addition, virt-sparsify exits with a non-zero status
code if there was a fatal error.

=back

All versions of virt-sparsify have supported the I<--machine-readable>
option.

=head1 EXIT STATUS

This program returns 0 if successful, or non-zero if there was an
error.

=head1 ENVIRONMENT VARIABLES

=over 4

=item TMPDIR

Location of the temporary directory used for the potentially large
temporary overlay file.

You should ensure there is enough free space in the worst case for a
full copy of the source disk (I<virtual> size), or else set C<$TMPDIR>
to point to another directory that has enough space.

This defaults to C</tmp>.

Note that if C<$TMPDIR> is a tmpfs (eg. if C</tmp> is on tmpfs, or if
you use C<TMPDIR=/dev/shm>), tmpfs defaults to a maximum size of
I<half> of physical RAM.  If virt-sparsify exceeds this, it will hang.
The solution is either to use a real disk, or to increase the maximum
size of the tmpfs mountpoint, eg:

 mount -o remount,size=10G /tmp

=back

For other environment variables, see L<guestfs(3)/ENVIRONMENT VARIABLES>.

=head1 SEE ALSO

L<virt-filesystems(1)>,
L<virt-df(1)>,
L<virt-resize(1)>,
L<virt-rescue(1)>,
L<guestfs(3)>,
L<guestfish(1)>,
L<truncate(1)>,
L<fallocate(1)>,
L<qemu-img(1)>,
L<http://libguestfs.org/>.

=head1 AUTHOR

Richard W.M. Jones L<http://people.redhat.com/~rjones/>

=head1 COPYRIGHT

Copyright (C) 2011-2012 Red Hat Inc.