VirtualBox

Ticket #17461 (new defect)

Opened 5 years ago

Last modified 4 years ago

writethrough affected by snapshots

Reported by: Loafer Owned by:
Component: virtual disk Version: VirtualBox 5.2.4
Keywords: Cc:
Guest type: Windows Host type: Windows

Description

I made this critical because not everyone will check for correct functionality. Restoring a snapshot will cause an unexpected data loss on a drive of type writethrough.

I've got a VM with a main drive and an attached writethrough drive. I see twice as many .vdi files than .sav files in the snapshot directory. And yes a restore changes the writethrough drive.

C:\Program Files\VirtualBox>VBoxManage showmediuminfo disk e:\dataw10.vdi
UUID: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Parent UUID: base
State: created
Type: writethrough
Location: E:\DataW10.vdi
Storage format: VDI Format
variant: fixed default
Capacity: 4096 MBytes
Size on disk: 4098 MBytes
Encryption: disabled
In use by VMs: Win10 (UUID: xxxxxxxxxxxxxxxxxxxxx)

Change History

comment:1 Changed 4 years ago by maxchen

This is not the problem of VB, but the guest Windows OS does CACHE the disk. See  https://forums.virtualbox.org/viewtopic.php?f=2&t=29136&p=439721#p130380

Once you restore the snapshot and restart the guest windows, please go offline and then online the writethrough disk (disconnect the drive and connect it back). For me, I will not use writethrough disk for windows guest again. I setup a hostonly network, and using smb (map network drive).

I hope the VB manual give a warning on this issue.

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