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Windows 7: What is a 'Shadow Copy'?

15 Dec 2014   #1
Melita

Windows 7 Home Premium 64bit
 
 
What is a 'Shadow Copy'?

In 'Backup and Restore' page of Windows 7, when I click on 'Create System Image' in the left navigation pane, a window comes up and says "Creating a Shadow Copy". Could you please tell me:

1. What is a 'Shadow Copy'?

2. Is it the same size as the system image or compressed?

3. Where is it stored?

4. Can I access this and transfer elsewhere for saving?

Thank you,


My System SpecsSystem Spec
.
15 Dec 2014   #2
ignatzatsonic

Microsoft Community Contributor Award Recipient

Windows 7 Home Premium SP1, 64-bit
 
 

Quote   Quote: Originally Posted by Melita View Post
In 'Backup and Restore' page of Windows 7, when I click on 'Create System Image' in the left navigation pane, a window comes up and says "Creating a Shadow Copy". Could you please tell me:

1. What is a 'Shadow Copy'?

2. Is it the same size as the system image or compressed?

3. Where is it stored?

4. Can I access this and transfer elsewhere for saving?

Thank you,
Shadow Copy - Wikipedia, the free encyclopedia

Above is something of an explanation. As I understand it, shadow copying is used by Windows Backup and also by Windows System Restore.

I don't use Windows Backup, but if I recall correctly the backup must be in its default location to restore properly. Is that the root of C?? I can't recall as I don't use it. I think you can move them, but before restoration you have to move them back to the default location.

System Restore points are relatively small. I have a dozen now and they take up 8 GB combined---whereas a single image file might take up 15 GB on my PC. System Restore points only back up certain types of Windows files.

I have no idea of the relative size of an image made by Windows Backup versus the size of an image made by some other program.

Windows Backup is too complex and finicky for me, so I just use another program.
My System SpecsSystem Spec
15 Dec 2014   #3
Kari

Microsoft Community Contributor Award Recipient

 

To put it very simple, a shadow copy when launching for instance system imaging creates a snapshot of the included drives in your image backup. This snapshot contains the information of the system at the moment of creating it, programs installed, file locations and so on.

Now when the imaging process starts the image is created according to this snapshot, changes you make to the system while imaging is running will be ignored. Although it is never a good idea to install and / or uninstall software while imaging, it gives a good example: let's say you launch Windows Image Backup and while it's running in the background you decide to install software, program XYZ. Image will be created in the background, at the same time program XYZ will be installed but because it is not included in snapshot, it will be excluded from the system image.

Snapshotting in this case is needed in order to let you to run image backup while at the same time utilizing your computer normally. The method is used widely by backup applications, an example of other programs using snapshotting is the Sysinternals Disk2VHD which creates a vhd of your Windows installation to be used as virtual machine.

Short: snapshotting, the shadow copy is widely used by tools and programs which create images of a running Windows system, be it for backup images or converting physical systems to virtual hard disks.

Kari
My System SpecsSystem Spec
.

15 Dec 2014   #4
Melita

Windows 7 Home Premium 64bit
 
 

Thank you very much for the lengthy explanation. That answers my first question.

My other 3 questions were with a view to saving a disk image in the HD of another computer. I have no external HD. I have full remote access to another computer. My idea was to save a System Image of Windows 7 in its own HD, and transfer it to the HD of the other computer. I have tried but this does not seem possible. Is there any way this can be done?

Regards,
My System SpecsSystem Spec
15 Dec 2014   #5
ignatzatsonic

Microsoft Community Contributor Award Recipient

Windows 7 Home Premium SP1, 64-bit
 
 

Quote   Quote: Originally Posted by Melita View Post
I have no external HD. I have full remote access to another computer. My idea was to save a System Image of Windows 7 in its own HD, and transfer it to the HD of the other computer. I have tried but this does not seem possible. Is there any way this can be done?

Regards,
I'd be skeptical, considering finicky Windows Backup is.

If I understand correctly, you have a PC and no external drive.

You want to make an image of the C drive of that PC and save it to some other drive, and then at some later date restore that image back to your PC if necessary.

Is that correct?

Where is this "in its own HD"? Another partition on the same drive? Another internal drive? Miles away on some network?

When you say "transfer", do you mean simply moving the unrestored image file from one drive to another? Or do you mean a Windows restoration process of some type?

You cannot save an image of a C partition on C.

You can save an image of a C partition on a D partition when both partitions are on the same hard drive.

Is that what you mean by "in its own HD"?

Images are generally of partitions, not of drives. That's why it's possible to save an image of C on the D partition. But that is not the best practice, because if that lone hard drive fails, you lose both your original C and your backup image on D.

An image file created with an application such as Macrium is just another file that can be moved around at will. Windows Backup frowns on that.

I'm not entirely clear on your plans, thus my questions above.
My System SpecsSystem Spec
15 Dec 2014   #6
Melita

Windows 7 Home Premium 64bit
 
 

If I understand correctly, you have a PC and no external drive

I have 2. Windows 7 and XP

You want to make an image of the C drive of that PC and save it to some other drive, and then at some later date restore that image back to your PC if necessary

Save it in XP and, Yes

Where is this "in its own HD"? Another partition on the same drive? Another internal drive? Miles away on some network?

Another partition in Win 7 Hard Drive C:

When you say "transfer", do you mean simply moving the unrestored image file from one drive to another?

Yes

You can save an image of a C partition on a D partition when both partitions are on the same hard drive.

Is that what you mean by "in its own HD"?


Yes

Images are generally of partitions, not of drives. That's why it's possible to save an image of C on the D partition. But that is not the best practice, because if that lone hard drive fails, you lose both your original C and your backup image on D

I will be moving it immediately to the Hard drive of XP

An image file created with an application such as Macrium is just another file that can be moved around at will

After wading through 'Windows Backup' page fruitlessly, It seems like this is the best option for me!
My System SpecsSystem Spec
15 Dec 2014   #7
ignatzatsonic

Microsoft Community Contributor Award Recipient

Windows 7 Home Premium SP1, 64-bit
 
 

Quote   Quote: Originally Posted by Melita View Post
[B]

I will be moving it immediately to the Hard drive of XP

An image file created with an application such as Macrium is just another file that can be moved around at will

After wading through 'Windows Backup' page fruitlessly, It seems like this is the best option for me!
I'd agree that Macrium is the better tool.

In the event of a disaster of some type, do you intend to restore the Win 7 image directly from the XP computer? Or move it back inside the Win 7 PC before restoration? I assume the Win 7 and XP computers are networked together in some way. I have no experience at all with how easily restoration over a network is with Macrium. Maybe trivially easy, maybe impossible. I dunno as my Macrium usage is strictly on a one PC setup (I store my images of C on a separate internal data hard drive and restore from that data drive. I also copy my unrestored images to another internal backup drive).
My System SpecsSystem Spec
15 Dec 2014   #8
whs
Microsoft MVP

Vista, Windows7, Mint Mate, Zorin, Windows 8
 
 

Here is a Macrium tutorial.

And do yourself a favpr and get an external disk (or a seperate internal disk) for the images. Best is a SSHD - those are the fastest spinning disks. An image of your system is not going to do you any good if it is on the same disk in a seperate partition the day the disk breaks down.

Btw - if you want to look at your shadows, run this command: vssadmin list shadows
My System SpecsSystem Spec
16 Dec 2014   #9
GeneO

Windows 10 Pro. EFI boot partition, full EFI boot
 
 

Quote   Quote: Originally Posted by Melita View Post
In 'Backup and Restore' page of Windows 7, when I click on 'Create System Image' in the left navigation pane, a window comes up and says "Creating a Shadow Copy". Could you please tell me:

1. What is a 'Shadow Copy'?
It is a point-in-time snapshot of the system, not a copy, so it is a misnomer. Copy on write is used. On a write , the old data that is going to be overwritten is first copied to the shadow copy area as a "diff" and the shadow copy references it instead of the new data (like an overlay). So data is copied, but only for writes that occur after the "shadow copy" was created. The file system at the time the shadow was made can be reconstructed from this "diff" data at any time by overlaying it over the file system, even though the file system has changed.

A clone can also be made of the whole system, but that doesn't make a lot of sense for backups or the system recovery "restore points". I don't know of any case where this is used - you wouldn't be able to access the system while it is copying like you can on copy on write.

Quote:

2. Is it the same size as the system image or compressed?
It can be from zero length, if no changes have been made to the file system, to large if many have. It depends on your activity.

Quote:

3. Where is it stored?
In a hidden system directory on the volume being shadowed.

Quote:

4. Can I access this and transfer elsewhere for saving?
Since it is not a copy, but differences - only disk blocks that have changed, making a copy doesn't make sense.It is an growing set of changes to the fs and not a static copy.

Quote:
Thank you,
Backups do make full copies of the file system, but by making a shadow copy "snapshot", then using it as the source, they can make a consistent point in time copy on a running system.


Macrium is good. I have never had it fail me and I have made dozens and dozens of restores.
My System SpecsSystem Spec
16 Dec 2014   #10
Melita

Windows 7 Home Premium 64bit
 
 

Quote   Quote: Originally Posted by whs View Post
Here is a Macrium tutorial.

And do yourself a favpr and get an external disk (or a seperate internal disk) for the images. Best is a SSHD - those are the fastest spinning disks. An image of your system is not going to do you any good if it is on the same disk in a seperate partition the day the disk breaks down.

Btw - if you want to look at your shadows, run this command: vssadmin list shadows
Thank you for the tutorial and other information. With Macrium, is it possible to make an image of the Operating System only, without other documents and user installed programs?

Quote   Quote: Originally Posted by GeneO View Post
Quote   Quote: Originally Posted by Melita View Post
In 'Backup and Restore' page of Windows 7, when I click on 'Create System Image' in the left navigation pane, a window comes up and says "Creating a Shadow Copy". Could you please tell me:

1. What is a 'Shadow Copy'?
It is a point-in-time snapshot of the system, not a copy, so it is a misnomer. Copy on write is used. On a write , the old data that is going to be overwritten is first copied to the shadow copy area as a "diff" and the shadow copy references it instead of the new data (like an overlay). So data is copied, but only for writes that occur after the "shadow copy" was created. The file system at the time the shadow was made can be reconstructed from this "diff" data at any time by overlaying it over the file system, even though the file system has changed.

A clone can also be made of the whole system, but that doesn't make a lot of sense for backups or the system recovery "restore points". I don't know of any case where this is used - you wouldn't be able to access the system while it is copying like you can on copy on write.

Quote:

2. Is it the same size as the system image or compressed?
It can be from zero length, if no changes have been made to the file system, to large if many have. It depends on your activity.

In a hidden system directory on the volume being shadowed.

Quote:

4. Can I access this and transfer elsewhere for saving?
Since it is not a copy, but differences - only disk blocks that have changed, making a copy doesn't make sense.It is an growing set of changes to the fs and not a static copy.

Quote:
Thank you,
Backups do make full copies of the file system, but by making a shadow copy "snapshot", then using it as the source, they can make a consistent point in time copy on a running system.


Macrium is good. I have never had it fail me and I have made dozens and dozens of restores
Thank you for the comprehensive explanation. I have been on to computers for only 3 years, but it never fails to amaze me at what they can do!

Something outside the topic; how can I make separate quotations from the same post as you have done above?

Thank you,

Kind regards,
My System SpecsSystem Spec
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