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=encoding utf8
=head1 NAME
virt-alignment-scan - Check alignment of virtual machine partitions
=head1 SYNOPSIS
virt-alignment-scan [--options]
virt-alignment-scan [--options] -d domname
virt-alignment-scan [--options] -a disk.img [-a disk.img ...]
=head1 DESCRIPTION
When older operating systems install themselves, the partitioning
tools place partitions at a sector misaligned with the underlying
storage (commonly the first partition starts on sector C<63>).
Misaligned partitions can result in an operating system issuing more
I/O than should be necessary.
The virt-alignment-scan tool checks the alignment of partitions in
virtual machines and disk images and warns you if there are alignment
problems.
Currently there is no virt tool for fixing alignment problems, except
to reinstall the operating system. The following NetApp document
summarises the problem and possible solutions:
L<http://media.netapp.com/documents/tr-3747.pdf>
=head1 OUTPUT
To run this tool on a disk image directly, use the I<-a> option:
$ virt-alignment-scan -a winxp.img
/dev/sda1 32256 512 bad (alignment < 4K)
$ virt-alignment-scan -a fedora16.img
/dev/sda1 1048576 1024K ok
/dev/sda2 2097152 2048K ok
/dev/sda3 526385152 2048K ok
To run the tool on a guest known to libvirt, use the I<-d> option and
possibly the I<-c> option:
# virt-alignment-scan -d RHEL5
/dev/sda1 32256 512 bad (alignment < 4K)
/dev/sda2 106928640 512 bad (alignment < 4K)
$ virt-alignment-scan -c qemu:///system -d Win7TwoDisks
/dev/sda1 1048576 1024K ok
/dev/sda2 105906176 1024K ok
/dev/sdb1 65536 64K ok
The output consists of 4 or more whitespace-separated columns. Only
the first 4 columns are signficant if you want to parse this from a
program. The columns are:
=over 4
=item col 1
the device and partition name (eg. C</dev/sda1> meaning the
first partition on the first block device)
=item col 2
the start of the partition in bytes
=item col 3
the alignment in bytes or Kbytes (eg. C<512> or C<4K>)
=item col 4
C<ok> if the alignment is best for performance, or C<bad> if the
alignment can cause performance problems
=item cols 5+
optional free-text explanation.
=back
The exit code from the program changes depending on whether poorly
aligned partitions were found. See L</EXIT STATUS> below.
If you just want the exit code with no output, use the I<-q> option.
=head1 OPTIONS
=over 4
=item B<--help>
Display brief help.
=item B<-a> file
=item B<--add> file
Add I<file> which should be a disk image from a virtual machine.
The format of the disk image is auto-detected. To override this and
force a particular format use the I<--format=..> option.
=item B<-c> URI
=item B<--connect> URI
If using libvirt, connect to the given I<URI>. If omitted, then we
connect to the default libvirt hypervisor.
If you specify guest block devices directly (I<-a>), then libvirt is
not used at all.
=item B<-d> guest
=item B<--domain> guest
Add all the disks from the named libvirt guest. Domain UUIDs can be
used instead of names.
=item B<--format=raw|qcow2|..>
=item B<--format>
The default for the I<-a> option is to auto-detect the format of the
disk image. Using this forces the disk format for I<-a> options which
follow on the command line. Using I<--format> with no argument
switches back to auto-detection for subsequent I<-a> options.
For example:
virt-alignment-scan --format=raw -a disk.img
forces raw format (no auto-detection) for C<disk.img>.
virt-alignment-scan --format=raw -a disk.img --format -a another.img
forces raw format (no auto-detection) for C<disk.img> and reverts to
auto-detection for C<another.img>.
If you have untrusted raw-format guest disk images, you should use
this option to specify the disk format. This avoids a possible
security problem with malicious guests (CVE-2010-3851).
=item B<-q>
=item B<--quiet>
Don't produce any output. Just set the exit code
(see L</EXIT STATUS> below).
=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.
=back
=head1 SHELL QUOTING
Libvirt guest names can contain arbitrary characters, some of which
have meaning to the shell such as C<#> and space. You may need to
quote or escape these characters on the command line. See the shell
manual page L<sh(1)> for details.
=head1 EXIT STATUS
This program returns:
=over 4
=item code 0
successful exit, all partitions are aligned E<ge> 64K for best performance
=item code 1
an error scanning the disk image or guest
=item code 2
successful exit, some partitions have alignment E<lt> 64K which can result
in poor performance on high end network storage
=item code 3
successful exit, some partitions have alignment E<lt> 4K which can result
in poor performance on most hypervisors
=back
=head1 SEE ALSO
L<guestfs(3)>,
L<guestfish(1)>,
L<virt-filesystems(1)>,
L<http://libguestfs.org/>.
=head1 AUTHOR
Richard W.M. Jones L<http://people.redhat.com/~rjones/>
=head1 COPYRIGHT
Copyright (C) 2011 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.
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