** Description changed:

  UserManual.pdf wrong about deleting snapshot - data from deleted
  snapshot does not merges with parent.
  
  Instead, data from deleted snapshot merges with all of its child
  snapshots.
- 
  
  Wrong information located into UserManual.pdf:
  -----------------------------------
  5.5 Differencing images
  ......
  If you later delete a snapshot in order to free disk space, for each disk 
attachment, one of
  the differencing images becomes obsolete. In this case, the differencing 
image of the disk
  attachment cannot simply be deleted. Instead, VirtualBox needs to look at 
each sector of
  the differencing image and needs to copy it back into its parent; this is 
called “merging”
  images and can be a potentially lengthy process, depending on how large the 
differencing
  image is. It can also temporarily need a considerable amount of extra disk 
space, before
  the differencing image obsoleted by the merge operation is deleted.
  -----------------------------------
  
  What exactly wrong in text above: "VirtualBox needs to...copy it back
  into its parent"
  
- 
  But really things are as follow. Imagine the situation:
  
  1. Create new virtual machine with windows XP using existing VDI disk image
-     (fresh installed system)
+     (fresh installed system)
  
  2. Create "clean" snapshot right after VM creation wizard have finished.
  
  3. Run the virtual machine, do some experiment and turn off it (Start
  menu, Shutdown)
  
  4. Right click to the "current state" and do "Take Snapshort", name it
  "after first experiment".
  
- 
  Now you will have following snapshots hierarchy:
  
  (Hint: you can see size of snapshots in "Virtual Media Manager")
  
  XP.vdi   - normal VDI, attached to "clean" snapshot (for ex, 1.2 Gb)
- -- {234234}  difference VDI, attached to "after first experiment" snapshot 
(for ex, 800 Mb)
+ -- {234234}  difference VDI, attached to "experiment 1" snapshot (for ex, 800 
Mb)
  ----{423412} difference VDI, attached to "XP" (current state, for example, 
168 Kb)
  
+ Question: what will happens if I delete "experiment 1" snapshot now?
  
- Question: what will happens if I delete "after first experiment" snapshot now?
- 
- According to the documentation (see quotation above) data from "after
- first experiment" will be merged to its parent- "clean" snapshot.
+ According to the documentation (see quotation above) data from
+ "experiment 1" will be merged to its parent- "clean" snapshot.
  
  But it really merges to "current state" snapshot, so after delete we
- will get:
+ will get following snapshots hierarchy:
  
- XP.vdi   - normal VDI, attached to "clean" snapshot (for ex, 1.2 Gb)
- --{423412} difference VDI, attached to "XP" (current state, for example, 802 
Kb)
+ 
+ XP.vdi - normal VDI, attached to "clean" snapshot (for ex, 1.2 Gb)
+ --{423412} diff VDI, attached to "XP" (current state, 802 Mb)
  
  
  
  More more, if you had following hierarchy:
  
  XP.vdi   - normal VDI, attached to "clean" snapshot (for ex, 1.2 Gb)
- -- {234234}  difference VDI, attached to "after first experiment" snapshot 
(for ex, 800 Mb)
- ---- {63453}  difference VDI, attached to "after second experiment a " 
snapshot (for ex, 30 Mb)
- ---- {32344}  difference VDI, attached to "after second experiment b " 
snapshot (for ex, 20 Mb)
+ -- {234234}  diff VDI, attached to "experiment 1" snapshot (for ex, 800 Mb)
+ ---- {63453}  diff VDI, attached to "experiment 2a " snapshot (for ex, 30 Mb)
+ ---- {32344}  diff VDI, attached to "experiment 2b " snapshot (for ex, 20 Mb)
  ------{423412} difference VDI, attached to "XP" (current state, for example, 
168 Kb)
  
- Question: what will happend if you delete "after first experiment"
- snapshot?
+ Question: what will happend if you delete "experiment 1" snapshot?
  
- Of cause, it will not be merged with parent "clean" image.
+ Of cause, it will _not_ be merged with parent "clean" image.
  
- It will merged to _both_  "after second experiment a" and "after second
- experiment b":
+ It will merged into _both_  "experiment 2a" and "experiment 2b":
  
  XP.vdi   - normal VDI, attached to "clean" snapshot (for ex, 1.2 Gb)
- -- {63453}  difference VDI, attached to "after second experiment a " snapshot 
(for ex, 830 Mb)
- -- {32344}  difference VDI, attached to "after second experiment b " snapshot 
(for ex, 820 Mb)
- ----{423412} difference VDI, attached to "XP" (current state, for example, 
168 Kb)
+ -- {63453}  diff VDI, attached to "experiment 2a " (830 Mb)
+ -- {32344}  diff VDI, attached to "experiment 2b " (820 Mb)
+ ----{423412} diff VDI, attached to "XP" (current state, for example, 168 Kb)
+ 
  
  That how it works in VirtualBox 4.2.
+ 
+ 
  
  ProblemType: Bug
  DistroRelease: Ubuntu 13.04
  Package: virtualbox 4.2.10-dfsg-0ubuntu2
  ProcVersionSignature: Ubuntu 3.8.0-19.29-generic 3.8.8
  Uname: Linux 3.8.0-19-generic i686
  ApportVersion: 2.9.2-0ubuntu8
  Architecture: i386
  Date: Thu May  2 21:44:37 2013
  InstallationDate: Installed on 2013-05-02 (0 days ago)
  InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release i386 (20130424)
  MarkForUpload: True
  ProcEnviron:
-  TERM=xterm
-  PATH=(custom, no user)
-  XDG_RUNTIME_DIR=<set>
-  LANG=ru_RU.UTF-8
-  SHELL=/bin/bash
+  TERM=xterm
+  PATH=(custom, no user)
+  XDG_RUNTIME_DIR=<set>
+  LANG=ru_RU.UTF-8
+  SHELL=/bin/bash
  SourcePackage: virtualbox
  UpgradeStatus: No upgrade log present (probably fresh install)

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https://bugs.launchpad.net/bugs/1175647

Title:
  UserManual.pdf wrong about deleting snapshot

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