Shadow Copies FAQ
Filed By: Robert Moir
Shadow Copies FAQ
Volume Shadow Copies - FAQ
Update available for the Volume Shadow Copy Service from Microsoft: Check this article, and if you have any of the problems listed in it, you can obtain a hotfix by contacting your local Microsoft support phone line and asking for the hotfix for KB Article 833167.
1. What is the Volume Shadow Copy Service?
The Volume Shadow Copy service, or VSS for short, is a new feature in Windows 2003 server that allows you to maintain multiple views of how files, folders and shares on a Windows 2003 server appeared in the past. At set times the VSS service takes a "snapshot" of how an area looks, and saves any differences between that snapshot and the previous snapshot for posterity.
2. Your point being...?
Ok, this is useful in a few ways, with some common ideas below:
- As a "network recycle bin" - An often requested feature in Microsoft Windows networks to recover work accidentally deleted.
- To enable easy review of multiple former versions of a document, including picking and choosing which version of a document (or even several versions) you wish to restore.
- To reduce "downtime" in backups of applications that lock lots of their files open during operation (typically database type apps). You can speed things up by taking a snapshot of the app's state quickly and bringing it online with little disruption to end users while you back up the contents of the snapshot in your own time.
3. What VSS is not
Well its not a substitute for proper backups and "data discipline". Obviously if you are storing the shadow copies on the same server as the originals then this doesn't help with disaster recovery. Nor is it all that efficient for restores of large amounts of files.
4. What do I need to run VSS?
VSS has two components. The first one is the volume shadow copy service on a Windows 2003 server system. The second is the VSS "Previous Versions" client, which needs to be running on all clients (and in some cases also on the server, see below).
5. What clients are compatible with VSS?
- Windows XP Pro
- Windows XP Home
- Windows 2000 (SP3 or higher)*
- Windows 98*
(To use with systems marked with a *, the client software must be installed on both the client and the Windows 2003 server holding the shadow volume).
6. What server requirements are there?
Well besides Windows 2003 standard, enterprise or datacentre configured in a file sharing role, and at least one NTFS volume? That's all you need from the software point of view.
From a hardware point of view, you'll want a lot of disk space to provide a VSS mirror of a lot of data. You do not need separate volumes for either the 'original data' volume or the volume where you store the shadow copies; you can put it all together on the same drive as the operating system if you like.
VSS works "On Write" which means that when you over-write a file on the volume being shadowed it takes a copy of any changed data, which obviously incurs a performance hit. For best performance I'd suggest storing the Operating system, Data Volume(s) and Shadow Copy Volume(s) on separate spindles from each other. Yes I know that's expensive considering you'd also want them all raided for reliability but if I start with what I feel is the absolute best solution you can look at that and look at your budget and draw your own compromise.
7. How does security work?
Well NTFS is a requirement of VSS, and VSS ACLs are preserved in shadow copies. If I've got access to the original file, I've got access to the shadow copies. If I don't have access to the original file, I don't have access to the shadow copies.
8. Is it Complicated?
VSS is designed so that once your IT department have setup VSS on the server, the VSS client can be deployed to workstations via GPOs (it comes as a MSI) or by your other preferred software deployment solution. Once its deployed, its very easy for normal end-users to use with maybe just a minimum of training.
9. Doesn't this all take a lot of disk space?
Well obviously it will have an impact, but two things are important to consider here. Server Administrators can impose limits on how much diskspace the shadow volumes will use with older shadow copies getting overwritten once the limit is reached.
More importantly, remember when I said that VSS only copies data that has changed in the answer to Question 6? VSS works by making a block-level copy of any changes that have occurred to files since the last shadow copy. Only the changes are copied, not the entire file.
As a result, the amount of space used up for each file's shadow copies can actually be quite small. How small exactly depends on the particular application. Some apps will work better with VSS in this regard than others.
10. Can I manipulate the shadow copy system via the command line or scripts?
Sure. The vssadmin command lets you manipulate the VSS subsystem and the schtasks command lets you manipulate scheduled tasks. Using a combination of those two commands and a bit of creativity the world is your oyster.
11. I'm having problems backing up Exchange 2003 and my system state with the shadow copy service.
To cut a long story short, if you have your information store on your operating system volume you are going to have to either move the information store onto another volume or set up two backup jobs so that you are not trying to do the system state and the exchange backup in the same job.
I'm going to be boring and refer you to a Microsoft knowledge base article for more information here:
http://support.microsoft.com/?kbid=820852 "Backup of the Exchange Server 2003 Information Store and the Windows Server 2003 System State Data Does Not Complete Successfully and Event ID 8019 Is Logged".
12. I'm sitting at the server desktop and I can't seem to find the previous versions tab in explorer?
Simple explanation for those who just want an answer to their problem and found this page with google:
For VSS to work you have to access your shadowed files as if you were connecting over the network, accessing them through the local explorer will not work. Simply connect to the share either via a mapped drive or a UNC path as if you were at a workstation and all will be fine.
Complex explanation for those who want to know more about how this stuff works:
VSS relies on Microsoft's Common Internet File System (CIFS) to work, which means you have to access the target folder from the network in order to use it. To do this from the local console you can simply open 'My Computer' and type in the server's name and the administrative share name for that volume, e.g. \\servername\vssrootdrive$ and then browse the target volume from there.
