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Diffstat (limited to 'qemu-img.texi')
| -rw-r--r-- | qemu-img.texi | 84 |
1 files changed, 27 insertions, 57 deletions
diff --git a/qemu-img.texi b/qemu-img.texi index 60b83fc11a..00fca8da86 100644 --- a/qemu-img.texi +++ b/qemu-img.texi @@ -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. -@end table +@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. -@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. +This option can only be enabled if @code{compat=1.1} is specified. -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. +@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 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 |