/[qemu]/qemu/qemu-doc.texi
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revision 1.48 by bellard, Sun Oct 3 14:33:10 2004 UTC revision 1.49 by bellard, Mon Nov 15 22:57:26 2004 UTC
# Line 584  CPU registers by prefixing them with @em Line 584  CPU registers by prefixing them with @em
584  @node disk_images  @node disk_images
585  @section Disk Images  @section Disk Images
586    
587  @subsection Raw disk images  Since version 0.6.1, QEMU supports many disk image formats, including
588    growable disk images (their size increase as non empty sectors are
589    written), compressed and encrypted disk images.
590    
591  The disk images can simply be raw images of the hard disk. You can  @subsection Quick start for disk image creation
592  create them with the command:  
593    You can create a disk image with the command:
594  @example  @example
595  dd of=myimage bs=1024 seek=mysize count=0  qemu-img create myimage.img mysize
596  @end example  @end example
597  where @var{myimage} is the image filename and @var{mysize} is its size  where @var{myimage.img} is the disk image filename and @var{mysize} is its
598  in kilobytes.  size in kilobytes. You can add an @code{M} suffix to give the size in
599    megabytes and a @code{G} suffix for gigabytes.
600    
601    @xref{qemu_img_invocation} for more information.
602    
603  @subsection Snapshot mode  @subsection Snapshot mode
604    
605  If you use the option @option{-snapshot}, all disk images are  If you use the option @option{-snapshot}, all disk images are
606  considered as read only. When sectors in written, they are written in  considered as read only. When sectors in written, they are written in
607  a temporary file created in @file{/tmp}. You can however force the  a temporary file created in @file{/tmp}. You can however force the
608  write back to the raw disk images by pressing @key{C-a s}.  write back to the raw disk images by using the @code{commit} monitor
609    command (or @key{C-a s} in the serial console).
 NOTE: The snapshot mode only works with raw disk images.  
   
 @subsection Copy On Write disk images  
   
 QEMU also supports user mode Linux  
 (@url{http://user-mode-linux.sourceforge.net/}) Copy On Write (COW)  
 disk images. The COW disk images are much smaller than normal images  
 as they store only modified sectors. They also permit the use of the  
 same disk image template for many users.  
   
 To create a COW disk images, use the command:  
   
 @example  
 qemu-mkcow -f myrawimage.bin mycowimage.cow  
 @end example  
610    
611  @file{myrawimage.bin} is a raw image you want to use as original disk  @node qemu_img_invocation
612  image. It will never be written to.  @subsection @code{qemu-img} Invocation
613    
614  @file{mycowimage.cow} is the COW disk image which is created by  @include qemu-img.texi
 @code{qemu-mkcow}. You can use it directly with the @option{-hdx}  
 options. You must not modify the original raw disk image if you use  
 COW images, as COW images only store the modified sectors from the raw  
 disk image. QEMU stores the original raw disk image name and its  
 modified time in the COW disk image so that chances of mistakes are  
 reduced.  
   
 If the raw disk image is not read-only, by pressing @key{C-a s} you  
 can flush the COW disk image back into the raw disk image, as in  
 snapshot mode.  
   
 COW disk images can also be created without a corresponding raw disk  
 image. It is useful to have a big initial virtual disk image without  
 using much disk space. Use:  
   
 @example  
 qemu-mkcow mycowimage.cow 1024  
 @end example  
   
 to create a 1 gigabyte empty COW disk image.  
   
 NOTES:  
 @enumerate  
 @item  
 COW disk images must be created on file systems supporting  
 @emph{holes} such as ext2 or ext3.  
 @item  
 Since holes are used, the displayed size of the COW disk image is not  
 the real one. To know it, use the @code{ls -ls} command.  
 @end enumerate  
   
 @subsection Convert VMware disk images to raw disk images  
   
 You can use the tool @file{vmdk2raw} to convert VMware disk images to  
 raw disk images directly usable by QEMU. The syntax is:  
 @example  
 vmdk2raw vmware_image output_image  
 @end example  
615    
616  @section Network emulation  @section Network emulation
617    

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