motorhead/qemu
1
0
Fork 0
mirror of https://github.com/Motorhead1991/qemu.git synced 2025-08-09 02:24:58 -06:00
Code Issues Projects Releases Packages Wiki Activity Actions

Documentation: Update image format information

Browse source 
Document new and yet undocumented options and image formats. The
qemu-img man page contains information only for raw and qcow2 now and
references the HTML documentation for a more detailed description of
other formats.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Kevin Wolf 2012-11-21 14:21:47 +01:00
parent a13e5e0557
commit d3067b020b
2 changed files with 196 additions and 59 deletions
Download patch file Download diff file Expand all files Collapse all files

88
qemu-img.texi
View file

@ -226,7 +226,10 @@ After using this command to grow a disk image, you must use file system and
partitioning tools inside the VM to actually begin using the new space on the
device.
@end table
@c man end
@ignore
@c man begin NOTES
Supported image file formats:
@table @option
@ -247,6 +250,13 @@ support of multiple VM snapshots.
Supported options:
@table @code
@item compat
Determines the qcow2 version to use. @code{compat=0.10} uses the traditional
image format that can be read by any QEMU since 0.10 (this is the default).
@code{compat=1.1} enables image format extensions that only QEMU 1.1 and
newer understand. Amongst others, this includes zero clusters, which allow
efficient copy-on-read for sparse images.
@item backing_file
File name of a base image (see @option{create} subcommand)
@item backing_fmt
@ -267,73 +277,33 @@ Preallocation mode (allowed values: off, metadata). An image with preallocated
metadata is initially larger but can improve performance when the image needs
to grow.
@item lazy_refcounts
If this option is set to @code{on}, reference count updates are postponed with
the goal of avoiding metadata I/O and improving performance. This is
particularly interesting with @option{cache=writethrough} which doesn't batch
metadata updates. The tradeoff is that after a host crash, the reference count
tables must be rebuilt, i.e. on the next open an (automatic) @code{qemu-img
check -r all} is required, which may take some time.
This option can only be enabled if @code{compat=1.1} is specified.
@end table
@item qed
Image format with support for backing files and compact image files (when your
filesystem or transport medium does not support holes). Good performance due
to less metadata than the more featureful qcow2 format, especially with
cache=writethrough or cache=directsync. Consider using qcow2 which will soon
have a similar optimization and is most actively developed.
@item Other
QEMU also supports various other image file formats for compatibility with
older QEMU versions or other hypervisors, including VMDK, VDI, VHD (vpc), qcow1
and QED. For a full list of supported formats see @code{qemu-img --help}.
For a more detailed description of these formats, see the QEMU Emulation User
Documentation.
Supported options:
@table @code
@item backing_file
File name of a base image (see @option{create} subcommand).
@item backing_fmt
Image file format of backing file (optional). Useful if the format cannot be
autodetected because it has no header, like some vhd/vpc files.
@item cluster_size
Changes the cluster size (must be power-of-2 between 4K and 64K). Smaller
cluster sizes can improve the image file size whereas larger cluster sizes
generally provide better performance.
@item table_size
Changes the number of clusters per L1/L2 table (must be power-of-2 between 1
and 16). There is normally no need to change this value but this option can be
used for performance benchmarking.
@end table
@item qcow
Old QEMU image format. Left for compatibility.
Supported options:
@table @code
@item backing_file
File name of a base image (see @option{create} subcommand)
@item encryption
If this option is set to @code{on}, the image is encrypted.
@end table
@item cow
User Mode Linux Copy On Write image format. Used to be the only growable
image format in QEMU. It is supported only for compatibility with
previous versions. It does not work on win32.
@item vdi
VirtualBox 1.1 compatible image format.
@item vmdk
VMware 3 and 4 compatible image format.
Supported options:
@table @code
@item backing_fmt
Image format of the base image
@item compat6
Create a VMDK version 6 image (instead of version 4)
@end table
@item vpc
VirtualPC compatible image format (VHD).
@item cloop
Linux Compressed Loop image, useful only to reuse directly compressed
CD-ROM images present for example in the Knoppix CD-ROMs.
The main purpose of the block drivers for these formats is image conversion.
For running VMs, it is recommended to convert the disk images to either raw or
qcow2 in order to achieve good performance.
@end table
@c man end
@ignore
@setfilename qemu-img
@settitle QEMU disk image utility