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Lady Fitzgerald
Starting Member

USA
9 Posts

Posted - November 18 2012 :  01:46:41  Show Profile  Reply with Quote
Is it ok to do work on the computer while MR is making an image?

Jeannie

et_and_family
Advanced Member

United Kingdom
500 Posts

Posted - November 18 2012 :  08:40:57  Show Profile  Reply with Quote
Hi

Yes, no problem Macrium Reflect will run in the background while you use your computer.

Regards

et
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Drac144
Advanced Member

USA
647 Posts

Posted - November 18 2012 :  21:10:55  Show Profile  Reply with Quote
I am not sure if this is a simple yes or no. Maybe someone else can comment. Aside from the obvious possibility of slowing down whatever work you are doing, or your work slowing down the backup, there is the question of causing changes to data while it is being backed up.

If you are doing an image backup, VSS will protect some of the data, but I do not believe it protects everything. I do not know whether copying data from one file to another or updating a Word or Outlook file could cause an issue with data during the backup.

If you are surfing the web or reading emails (without changing or deleting) that should certainly be OK. Just to be safe, I always do backups when I am going to be away from my computer. I do incremental backups while working on my computer but since they typically take less than 5 minutes, I am less concerned that something I do could cause an issue.
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alan9182
Advanced Member

United Kingdom
527 Posts

Posted - November 18 2012 :  21:22:17  Show Profile  Reply with Quote
et
Sorry to break in here, but is it always true ?

I know it should be if VSS is running properly,
but I have an idea that Macrium has an alternative mechanism that may come into play if the Windows VSS is broken,
and I do not know if the alternative is as bullet proof.

I sent a P.M. to you but I think the forum P.M. is broken and it has sent back a message
Re: (Case 23735) Sent From Macrium Support Forum by alan9182
Please note that the free edition of Macrium Reflect is not a supported product.


Jeannie
I suggest you wait for et or other experts to advise whether my fear is groundless.
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Lady Fitzgerald
Starting Member

USA
9 Posts

Posted - November 19 2012 :  05:00:38  Show Profile  Reply with Quote
quote:
Originally posted by Drac144

I am not sure if this is a simple yes or no. Maybe someone else can comment. Aside from the obvious possibility of slowing down whatever work you are doing, or your work slowing down the backup, there is the question of causing changes to data while it is being backed up...


I had kinda suspected that any data changes probably wouldn't get picked up in the image if the location of the data had already been added to the image.

quote:
Originally posted by Drac144

...If you are doing an image backup, VSS will protect some of the data, but I do not believe it protects everything. I do not know whether copying data from one file to another or updating a Word or Outlook file could cause an issue with data during the backup...


I have no clue what VSS is or what it does.

quote:
Originally posted by Drac144

...If you are surfing the web or reading emails (without changing or deleting) that should certainly be OK. Just to be safe, I always do backups when I am going to be away from my computer. I do incremental backups while working on my computer but since they typically take less than 5 minutes, I am less concerned that something I do could cause an issue.



That was pretty much what I had in mind. A full image takes roughly 2 1/2 hours using a internal type HDD in a USB 2.0 dock; a differential takes around half an hour. I frequently fire up Media Monkey to play music when I go to bed and set it to shut off the computer after playing for a couple of hours (I read for a while before killing the lights and rolling over to sleep). I was thinking I could run differentials and let Media Monkey shut down the computer since it takes less time to run the differential. When running a new full image, I could just let Media Monkey run for the two hours then just shut itself off, then let Reflect shut down the computer when it is done. I could then just put away the HDD and dock in the morning before firing the computer up again.

Jeannie

Edited by - Lady Fitzgerald on November 19 2012 05:02:50
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Lady Fitzgerald
Starting Member

USA
9 Posts

Posted - November 19 2012 :  05:01:51  Show Profile  Reply with Quote
quote:
Originally posted by alan9182

...Jeannie
I suggest you wait for et or other experts to advise whether my fear is groundless.




Ok, waiting.

Jeannie
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alan9182
Advanced Member

United Kingdom
527 Posts

Posted - November 19 2012 :  10:34:52  Show Profile  Reply with Quote
VSS is special magic which I try not to think about.

This is a fairly short explanation which is the simplest I have ever seen
http://msdn.microsoft.com/en-gb/library/windows/desktop/aa384612%28v=vs.85%29.aspx
It holds a caution :-
quote:

Default Shadow Copy State

Even though the file system flushes all I/O buffers prior to creating a shadow copy, this will not ensure that incomplete I/O is properly handled.


My interpretation :-
Any music that you are downloading are playing at the time you launch an image backup will not be "properly handled" - whatever that means,
but any downloading or playing that is initiated AFTER you launch the backup will be no problem.

For more technical explanations :-

This gives an overview
https://en.wikipedia.org/wiki/Shadow_Copy

This indicates to me that VSS will disable normal write access to any volume that it is protecting.
http://msdn.microsoft.com/en-us/library/windows/desktop/aa384623%28v=vs.85%29.aspx
I think I remember reading elsewhere that whilst write access is disabled it is somehow faked and held in abeyance until access is re-enabled.

Regards
Alan
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et_and_family
Advanced Member

United Kingdom
500 Posts

Posted - November 19 2012 :  11:06:13  Show Profile  Reply with Quote
Hi

I have scheduled Full Images and Incrementals and with both versions 4.2 and 5. I have always continued to work while backups take place without a problem (although computer may be slower at times). The software I have mainly been using is OUTLOOK 2010, Firefox, WORD, EXCEL, ACCESS, POWERPOINT, PUBLISHER, Adobe Photoshop Elements & PagePlus. Over the last few years I have never has a problem in continuing to use the computer.

The Microsoft products are VSS aware which might help.

I accept there may be exceptions and expect a reply from Macrium Support in due course to clarify the situation.

Regards

et
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Antony
Moderator

United Kingdom
212 Posts

Posted - November 19 2012 :  12:31:30  Show Profile  Reply with Quote
Hi All,

Yes, you should be fine to continue using your computer during a backup.

To clarify what is going on, Microsoft's VSS operates by taking what is called a copy on write snapshot of your system. This allocates a small temporary storage space. Then, every time you write to your disk, the current data is copied to the snapshot before the new data is written in.

In reverse, when reading a snapshot, Windows provides Reflect with either the old data from the snapshot if that area of the disk has been written to, or the data on the disk if it is unchanged.

As such, VSS provides a point-in-time snapshot of your system which is consistent.

There is one issue to consider - the snapshot must store the previous data from the disk in a temporary location. The more writes, the more it must store. So, if you perform an excessive amount of disk activity during imaging, the snapshot storage space may become full. Reflect will then inform you of the error, as the snapshot cannot continue.

The space VSS uses for this snapshot is freed once the snapshot is finished with - in the case of Reflect when the backup operation finishes (successfully or otherwise).

So, VSS will allow you to take a consistent snapshot of your system at a given point in time. You can then continue working with that system. The only caveat is that you keep disk activity reasonable - de-fragmenting your hard disk during an image, or copying your DVD collection between two drives churning up gigabytes of data will be a problem, but ordinary web browsing, office application use, email, or even image editing will be fine. We regularly run images whilst developing in the office.

Kind Regards,

Antony
Macrium Support
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Lady Fitzgerald
Starting Member

USA
9 Posts

Posted - November 19 2012 :  14:06:00  Show Profile  Reply with Quote
Ok, thanks, guys! Seems the only restriction might be to abstain from downloading music when making an image, something I don't do anyway (Media Monkey plays from files already on the computer, not from streaming), so no worries. This will make imaging a lot easier for me.

Jeannie
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alan9182
Advanced Member

United Kingdom
527 Posts

Posted - November 20 2012 :  21:27:26  Show Profile  Reply with Quote
Antony

Thank you for an excellent explanation of VSS.
I understood it when I went to bed,
and I still understood it when I got up this morning.

I have seen many that are far more technical,
but required me to believe 6 impossible things before breakfast
e.g. it was implied that the copy to temporary storage was not "on demand",
but that at launch it took only a second to copy a 50 GB system partition in anticipation of the need.

I think elsewhere I have read that the temporary storage space is actually unused "free space" in the same partition that is being imaged.
Questions :-
Is that so when Reflect is using "Intelligent sector copy" ?
What temporary storage is used for "Make an exact copy of the partitions" ?

Incidentally, I think that when I was using version 4 there was a "fall-back" mechanism that was used should VSS be inoperative.
Does this happen with version 5, or is it guaranteed that an image is aborted upon VSS failure ?

Suggestion.

Please make this explanation as a FAQ sheet.
I think it would be a great benefit and source of assurance for many Reflect Users such as myself.

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Drac144
Advanced Member

USA
647 Posts

Posted - November 21 2012 :  01:49:12  Show Profile  Reply with Quote
Antony,

Thanks for the VSS explanation. After reading the link below I am even more confused.

http://searchdatabackup.techtarget.com/definition/VSS-based-backup

This link suggests that programs need to have VSS processes (at least pre and post) to correctly use VSS. So even if Reflect is sending out pre and post backup notices, if an application does not support those notifications, they will not handle VSS correctly.

You said that VSS is totally transparent to all apps. Please provide additional input on this issue.
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Antony
Moderator

United Kingdom
212 Posts

Posted - November 21 2012 :  11:22:05  Show Profile  Reply with Quote
Hi All,

Alan, you are correct. On 32-bit XP systems only, we have a driver called pssnap.sys which provides copy-on-write again. This works in a very similar way to VSS, but does not supply all of VSS's features, so we opted to use VSS. Another strongly motivating reason for using VSS was that it is supported by Microsoft and a core part of all Windows OSes greater than XP SP2 - as such, we know we can rely on it.

In terms of the storage space used, yes, VSS uses space on a drive as per its configuration. This does not have to be the same drive as is being imaged. VSS is smart enough to know to not include this temporary storage in the snapshot it makes. After all, it has to know where the snapshot copies of any data are written to. It also excludes any previous snapshots you have made from the snapshot.

Intelligent sector copy is slightly different. This is how we read the data from the disk - there are basically two ways to do this: 1, read it all including zeros and massive areas of free space, and 2) read only what is in use. Sometimes, you may wish to read it all, in what we call a forensic copy, because you wish to preserve what is in the free space for analysis of, say, malware, but normally you just want the data.

Drac, there are three components to any VSS operation. The requester is, as you'd expect, the application asking for a snapshot to begin. In our case, Reflect is a requestor. There is a VSS provider which implements the core parts of VSS - normally, the Microsoft VSS provider is sufficient for most solutions and this is what we use.

Finally, there are VSS writers. These components provide a mechanism for applications to be alerted to the creation of a snapshot, so they can prepare their data for snapshotting. This is important in enterprise scenarios, for example if you are running a high-load transactional database or a virtual machine cluster. In this case, the disk is under heavy load and the application is storing some of its state on disk too. Taking a snapshot of that information as-is would not necessarily give you a consistent backup. VSS writers exist to inform these applications to tidy up, and then to alert them that the snapshot has been taken and they may continue.

Normal consumer applications have a very narrow IO bandwidth - they tend to write small discrete chunks of data, for example a word document or a settings file. The OS and VSS is not stressed by this at all, and the IO will have completed before the snapshot is created even if the application is not VSS aware. Alternatively, it will not have been saved before snapshot creation and will then be present in the next backup. You would have to try very very hard to create a snapshot of half a saved word document, because the OS and VSS are designed to try to not let that happen, and with IO that small, they can.

So, it comes down to - if you're running a workstation with several VMs and perhaps a local database server, you might want to look into whether your VM software provides VSS writers (VMware/Hyper-V do, for example) if you want these included in your snapshot. Likewise, you might want to consider the same for your database if it is under high load (continually serving requests - a database server used for development would not be enough). A normal consumer writing a word document or excel spreadsheet would be fine.

Hope that clears things up,

Antony
Macrium Support

Edited by - Antony on November 21 2012 11:22:23
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alan9182
Advanced Member

United Kingdom
527 Posts

Posted - November 21 2012 :  14:35:33  Show Profile  Reply with Quote
I would like to know where the temporary space is located.

Assuming that C:\ is a 50 GB partition with 30 GB of free space,
and a very important file was accidentally deleted before it was backed up,
and my only hope is to use file recovery software to retrieve it from free space,
then I might wish to "Make an exact copy of the partitions" so that if freeware file recovery fails to work and further over-writes the contents of free space then I can restore free space to improve prospects of recovery by commercial software.

Question :-
Whilst "exact copy of the partitions" is under way,
if I download a file and it is deflected by the VSS system into temporary storage until the copy is conclude,
is this file going to temporarily occupy space in my 8 GB of RAM,
or would it be held in "free-space" and thus over-write part of the disk that I need to recovery the deleted file from.

I am think a 3 GB download stands a 10% chance of over-writing the important deleted file that is somewhere in 30 GB free space.

In the above situation I would naturally minimize any action that would but recovery at risk,
but I would rather know exactly what actions will hurt me and how rather than live in fear of the unknown.

Regards
Alan
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Nick
Moderator

United Kingdom
6303 Posts

Posted - November 21 2012 :  15:14:32  Show Profile  Reply with Quote
Hi Alan

Thanks for your post.

Any new files created during the backup cause existing file system clusters to be saved to the shadow copy storage area file. This is a temporary file located under '\System Volume Information'.

As with all new file disk activity, this will reduce the chance of 100% recovery of a deleted file if you run an 'un-delete' tool on the restored partition. It also depends at what point in the backup the activity occurs. If the disk sectors have already been backed up then it won't be an issue if not then it may.

Kind regards

Nick - Macrium Support


Edited by - Nick on November 21 2012 16:16:46
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alan9182
Advanced Member

United Kingdom
527 Posts

Posted - November 21 2012 :  21:59:52  Show Profile  Reply with Quote
Thanks,
I really think I have no more questions on VSS.
All the fuzzy loose ends have been tied up.

Yikes
On 32 bit XP I disliked the aggravation of Restore Points being created on my non-system partition that held Internet downloads.
I disabled monitoring and after a couple of reboots it was monitored again.
I used CACLS to take ownership of '\System Volume Information'
and then I deleted that folder and replaced it with a write protected file by the same name.
That stopped the Restore Point tom foolery.

I really must remember not to be so adventurous with 64 bit Win 7.
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