Snapshots and Writethrough

Discussions about using Windows guests in VirtualBox.

Snapshots and Writethrough

Postby Demiourgos » 20. Mar 2010, 22:49

I have an XP guest on a normal vdi drive and documents on a writethrough drive. I have copied some files on the documents disk but after snapshot restore they were lost. I can't do anything with this. I can't use NFS and ISCSI drive (through the MS ISCSI initiator on the guest) doesn't work properly after restores. Are there any ideas about the subject?
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Re: Snapshots and Writethrough

Postby Perryg » 21. Mar 2010, 00:40

I have an XP guest on a normal vdi drive and documents on a writethrough drive

Is this write through drive another VDI that you have attached and marked as writethrough?
If so these are not included in the snapshot and should not be touched when you revert or delete snap shots.
Explain a little more about how these were created and also post the following information about the guest in question.
From the host terminal/command windows VBoxManage showvminfo <VM Name> --details --machinereadable and post here. Replace <VM Name> with the actual name of the VM. Use "" if the name has a space in it.
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Re: Snapshots and Writethrough

Postby Demiourgos » 22. Mar 2010, 11:10

I tried VDI and ISCSI (both marked as writethrough, cache on windows guest is turned off), but the result is the same. I make a snapshot, then copy files, restore snapshots, see no files at all.

Code: Select all   Expand viewCollapse view
name="Test"
ostype="WindowsXP"
UUID="7c484d4f-765b-4c59-a9d1-15c071f9a1ed"
CfgFile="G:\VD\.VirtualBox\Machines\Test\Test.xml"
hardwareuuid="7c484d4f-765b-4c59-a9d1-15c071f9a1ed"
memory=1536
vram=32
cpus=2
synthcpu="off"
bootmenu="messageandmenu"
boot1="floppy"
boot2="dvd"
boot3="disk"
boot4="none"
acpi="on"
ioapic="on"
pae="on"
biossystemtimeoffset=0
hwvirtex="on"
hwvirtexexcl="off"
nestedpaging="on"
vtxvpid="off"
VMState="running"
VMStateChangeTime="2010-03-22T09:01:09.732000000"
monitorcount=1
accelerate3d="on"
accelerate2dvideo="on"
teleporterenabled="off"
teleporterport=0
teleporteraddress=""
teleporterpassword=""
storagecontrollername0="IDE Controller"
storagecontrollertype0="PIIX4"
storagecontrollerinstance0="0"
storagecontrollermaxportcount0="2"
storagecontrollerportcount0="2"
storagecontrollername1="Floppy Controller"
storagecontrollertype1="I82078"
storagecontrollerinstance1="0"
storagecontrollermaxportcount1="1"
storagecontrollerportcount1="1"
storagecontrollername2="SATA ??????????"
storagecontrollertype2="IntelAhci"
storagecontrollerinstance2="0"
storagecontrollermaxportcount2="30"
storagecontrollerportcount2="3"
"IDE Controller-0-0"="none"
"IDE Controller-0-1"="none"
"IDE Controller-1-0"="C:\PROGRA~1\Sun\VIRTUA~1\VBoxGuestAdditions.iso"
"IDE Controller-ImageUUID-1-0"="69494da0-5e7b-4d69-9eac-a8bbc7ebe330"
"IDE Controller-1-1"="none"
"Floppy Controller-0-0"="emptydrive"
"Floppy Controller-0-1"="none"
"SATA ??????????-0-0"="G:\VD\.VirtualBox\Machines\Test\Snapshots\{a356d7d8-a9d
e-4d03-a92f-51c3eacb9a8b}.vdi"
"SATA ??????????-ImageUUID-0-0"="a356d7d8-a9de-4d03-a92f-51c3eacb9a8b"
"SATA ??????????-dvdpassthrough"="on"
"SATA ??????????-1-0"="127.0.0.1|iqn.WorkDoc2"
"SATA ??????????-ImageUUID-1-0"="13a2305c-4507-433f-8cd2-5f74cc9f3ea8"
"SATA ??????????-2-0"="g:\test.vdi"
"SATA ??????????-ImageUUID-2-0"="be7f4d31-40bd-48cb-9437-2836353672f7"
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Re: Snapshots and Writethrough

Postby Demiourgos » 22. Mar 2010, 11:13

UUID: be7f4d31-40bd-48cb-9437-2836353672f7
Accessible: yes
Description:
Logical size: 5120 MBytes
Current size on disk: 39 MBytes
Type: writethrough
Storage format: VDI
In use by VMs: Test (UUID: 7c484d4f-765b-4c59-a9d1-15c071f9a1ed)
Location: g:\test.vdi


The most interesting thing is that current size on disk is 39 mbytes. Just like it should be if the files are really there, but in windows there is nothing.
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Re: Snapshots and Writethrough

Postby Perryg » 22. Mar 2010, 15:10

These kinds of problems that are reproducible should be reported to bugtracker. You will need to setup an account there as it is on a different system.
It would also help if you can post the ticket number here so other can see the progress, add information, or see the final results.
Be sure to post your log file and this showinfo as an attachment (not in the main body of the ticket) they will need them both.
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Re: Snapshots and Writethrough

Postby Demiourgos » 24. Mar 2010, 14:40

I finally got it. This is the Windows XP guest problem (not VirtualBox) that appears only when restoring snapshots when writethrough or ISCSI (not Virtualbox but normal drive through the iscsi initiator) drive attached.
Windows has a filesystem cache or something like that and the only way to update it is disconnecting the drive and connecting it back. The solution I've found was using a snapshot with non-attached iscsi drive and connecting it right after restore. It's quite inconvinient but works good. Trying to use writethrough drives with WinXp guest will certainly result in corrupted filesystem. So be careful. If someone finds a better way please write here.
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Re: Snapshots and Writethrough

Postby jorgensen » 24. Mar 2010, 14:57

I also had a problem with snapshots and writethrough data drives, which turned out to be a bug in version 3.1.0.
After updating to 3.1.4 I haven't had a problem with this issue - uses AHCI interface for all XP drives.
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Re: Snapshots and Writethrough

Postby maxchen » 26. Jan 2019, 05:13

Demiourgos wrote:I finally got it. This is the Windows XP guest problem (not VirtualBox) that appears only when restoring snapshots when writethrough or ISCSI (not Virtualbox but normal drive through the iscsi initiator) drive attached.
Windows has a filesystem cache or something like that and the only way to update it is disconnecting the drive and connecting it back. The solution I've found was using a snapshot with non-attached iscsi drive and connecting it right after restore. It's quite inconvinient but works good. Trying to use writethrough drives with WinXp guest will certainly result in corrupted filesystem. So be careful. If someone finds a better way please write here.


I test this on Win 10 ltsc. Yeah, be careful! The data are there but if you write to disk in a state by restoring to previous snapshot, they may damage the disk.
To disconnect and then connect it back in Win 10: disk manager, offline, then online the disk
For this reason, writethrough is dangerous for snapshots. I would rather using man network driver to share the data between snapshots
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Re: Snapshots and Writethrough

Postby socratis » 5. Feb 2019, 18:13

@maxchen
Can you please explain to me, what value does an answer have to a semi-resolved topic after 9 years?
Do NOT send me Personal Messages (PMs) for troubleshooting, they are simply deleted.
Do NOT reply with the "QUOTE" button, please use the "POST REPLY", at the bottom of the form.
If you obfuscate any information requested, I will obfuscate my response. These are virtual UUIDs, not real ones.
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