Opened 6 years ago

Last modified 5 years ago

#17461 new defect

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


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 (1)

comment:1 by maxchen, 5 years ago

This is not the problem of VB, but the guest Windows OS does CACHE the disk. See

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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