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I am trying to setup a backup system at my work. We have an Windows 2012 environment with some VMs. We have a SAN and I tried do backups on a shared folder but, because of some incompatibilities with Samba versions, I changed this to iSCSI access.

At first glance, all is great. I can make individual backups from my VMs every time I want... but there is one thing that I dont understand.

Lets say I have two VM's on my Windows Server.

VM "A" have 30GB disk size;
VM "B" have 10GB disk size;

First, I made a backup of VM "A": All went well, on iSCSI I could see the files and a file with nearly 30GB size that I believe is VM "A" disk file.

Now, I made a backup of VM "B": The backup runs great but, on iSCSI folders, there are only a file with 10GB size that I believe is VM "B" disk file but, the early 30GB file is gone.

Ok... looks like wbadmin overwrited my first backup...

BUT...

When I tried to restore the first backup, all worked! I can restore both backups, even with the first 30GB backup file gone.

So, here is my question: Why can I restore the first backup? And where are the files that belongs to this backup?

Thanks!

Ederson
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1 Answers1

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Windows Server Backup uses Volume Shadow Copy Service (VSS) to maintain old versions of backups. You're not seeing the shadow copy reflected in the filesystem view of the backup folder, but the blocks that make up the old backup are still there (managed by VSS).

You can use the vssadmin list shadows command to show the shadow copies that exist on a volume.

Evan Anderson
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  • Windows Server Backup ensure that blocks aren't overwritten? – Ederson Oct 06 '14 at 19:00
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    Volume Shadow Copy Service (VSS) maintains copy-on-write snapshots of changed blocks in the volume. Windows Server Backup just leverages the functionality that VSS provides. – Evan Anderson Oct 06 '14 at 19:04