Selecting the input guest

You can run virt-v2v-inspector with the same -i* options as virt-v2v. (Don't use any -o* options). This will select the guest that you want to estimate.

For example to estimate the space required for a guest in a stored local disk called filename.img you could do:

 virt-v2v-inspector -i disk filename.img

Output

The output from this tool is an XML document.

• Fields which are annotated with an "estimated='true'" attribute are estimated. Virt-v2v cannot always know exactly the final size of some things, such as the exact real size of the output disk, since there might be small perturbations between runs. Estimates are usually very close to the final values.
• Numbers representing sizes are always given in bytes.
• By default the output is written to stdout. This is useful when using the program interactively. However if you want to use this tool from another program it is better to send the output to a specific file using -O output.xml

 <?xml version='1.0' encoding='utf-8'?>
 <v2v-inspection>
   <program>virt-v2v-inspector</program>
   <package>virt-v2v</package>
   <version>2.1.9</version>

The <program>, <package> and <version> elements refer to the current version of virt-v2v-inspector and are useful for debugging. Make sure you use the same version of virt-v2v-inspector and virt-v2v.

   <disks>
     <disk index='0'>
       <virtual-size>6442450944</virtual-size>
       <allocated estimated='true'>1400897536</allocated>
     </disk>
     <disk index='1'>
       <virtual-size>6442450944</virtual-size>
       <allocated estimated='true'>45131520</allocated>
     </disk>
   </disks>

The <disks> element lists information about each guest disk. The example virtual machine above has two disks. <virtual-size> describes the size of the disk as seen from inside the guest, while <allocated> is an estimate of how much storage will be needed on the host after conversion. This is assuming you use -oa sparse - see the notes below.

   <operatingsystem>
     <name>linux</name>
     <distro>fedora</distro>
     <osinfo>fedora32</osinfo>
     <arch>x86_64</arch>
     [...]
   </operatingsystem>

The <operatingsystem> element lists information about the guest operating system gleaned during conversion, in a manner similar to the virt-inspector(1) tool from guestfs-tools.

Output allocation mode and output format

Virt-v2v supports selecting the output allocation mode (-oa option) and output format (-of option, eg. -of qcow2). Since it is difficult to predict the effect of these options on the actual space occupied by the final image this tool does not account for them.

As a rule of thumb:

virt-v2v -oa preallocated

causes the disk images on the target to consume their full virtual size (excluding the effect of zero allocations will depends so much on the underlying storage that it is often hard even for experts to predict).

virt-v2v -of qcow2

uses the QCOW2 format where supported which means that the apparent size of the file will be equal to its sparse size, but otherwise should not affect estimates very much.