Public bug reported:
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)
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 "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?
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 following snapshots hierarchy:
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} 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 "experiment 1" snapshot?
Of cause, it will _not_ be merged with parent "clean" image.
It will merged into _both_ "experiment 2a" and "experiment 2b":
XP.vdi - normal VDI, attached to "clean" snapshot (for ex, 1.2 Gb)
-- {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
SourcePackage: virtualbox
UpgradeStatus: No upgrade log present (probably fresh install)
** Affects: virtualbox (Ubuntu)
Importance: Undecided
Status: New
** Tags: apport-bug i386 raring
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https://bugs.launchpad.net/bugs/1175647
Title:
UserManual.pdf wrong about deleting snapshot
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