What happens when a file is in use during backup
When performing an image backup while a computer is in use, how does Acronis deal with files that are in use during the backup operation? Here are some related specific questions:
1. What if a file is in use when Acronis goes to back it up during the backup operation?
2. What if a file is backed up during the operation, but is edited and changes before the backup session is over?
3. What if a program, such as an accounting program, is in use in such a way that the application is continually updating multiple files or databases? In many cases, the whole related multi-file database needs to be backed up at the same time or the database file relationships may be corrupted.
Thank you for any help with this issue.
Hello Grover,
Thank you again for the reply. We follow your thinking, except that the "snapshot" example appears somewhat over-simplified. The backup process actually requires 1-2 hours on our system and, as such, is not an instantaneous snapshot. So, if the computer is in use during this 2-hour backup process, how does Acronis deal with the files, or disk sectors, that are in use by other applications during the backup process and presumably cannot be accessed by Acronis until free?
Off course, this dilemma is common to all 'backup program' developers, but we're wondering how Acronis deals with such anomalies. Does the program skip files in use, if so how do we know which files were skipped? Do they mark the files, or disk sectors in use, and come back to back them up when free? Does Acronis lock the whole disk or partition until finished? It is hard for us to have a sense of comfort until some of these questions can be explained.
Thanks
As I don't speak for Acronis, perhaps you might want to send the Acronis forum moderator a privage message referring to your question.
It doesn't skip files. Like Grover, I don't know all the technical details of how it works, but it works.
Thank you so much, Grover, we appreciate your candor. We will forward some of these questions to the moderator. Is there any other way for a user to forward these questions to technical support representative? Is there a period of free support following the initial purchase of the product? Also wanted to thank you for your insightful reply to other questions we posted.
Thanks
First 30 days of purchase is free support for customer issues. Thank you. Glad I was able to assist.
You can study Microsoft's Volume Shadow Copy Service (VSS) to learn about the snapshot process for backing up a live system. Acronis uses a similar service called snapman.sys to create the snapshot. The snapshot is taken at the very beginning of the backup process. It happens in a matter of seconds. Then the backup is done with all files in the condition they were in when the snapshot was taken. Any changes to files after the snapshot was taken will not be reflected in the backup.
You could have some fun to see if you can change a file after the backup starts and see if the change is made in the backed up file. For example, create a text file with the line "This is what the file looked like when the backup was stared." After the backup starts, add the line "This line was added after the backup was started." If the backup was a full disk or partition backup, you can mount the backup and look at the text file to see what it looks like.
1&2 - snapshot is taken at the beginning of backup process and all changes after it will not appear in backed up data.
3 - True Image doesn't use VSS, so database files (even of VSS-aware databases such as MS SQL server) may become inconsistent (crash-consistent, like if power was turned on during operation). Acronis Backup, including Acronis Backup for PC , use VSS by default.
Hello Everyone!
BlueMax, I'd like to add to the third point that even if your database doesn't support VSS it is more convenient to use Acronis Backup for PC than Acronis True Image to back it up. To keep a backup of your database consistent in case if it doesn't support VSS you'll have to stop the database before backup. But (!) Acronis True Image 2014 can use for this purpose pre/post backup commands and Acronis Backup for PC allows usage pre/post data capture commands. Please check this article for more information.
Thank you.
Thank you, Mustang, the information was most useful. We may even try your little experiment when we get a minute.
Any reason why Acronis Backup uses VSS, but True Image does not? Seems that True Image is the flagship product and should be equally concerned with such protections.
I'm a little curious why you recommend Acronis Backup over True Image for a PC? We had come to understand that Acronis True Image Premium was really one of your flagship products. Unfortunately, as a newcomer, we have had a problem distinguishing the differences between the two products. Can Acronis Backup restore a whole system including the operating system and programs?
Finally, what pre-backup commands would we use to close a program or database before the backup? Is there a reference or knowledgebase article relating to this subject?
Hello BlueMax,
Acronis Backup is just more convenient for backing up VSS-supporting databases than Acronis True Image 2014.
Acronis Backup and Acronis True Image are different product lines which are designed for different purposes.
Acronis True Image is supposed to be used in home and home office environments and Acronis Backup in business environment. This article can help you in making a decision which product you need:
As for batch files that can be used as pre/post commands, they are supposed to be written by user because they strongly depend on environment. Here we have some samples but please note that they should be adjusted to your scenario and environment.
Thank you.
Hi altogether,
I'd like to contribute an interesting fact to this thread. It seems that neither VSS nor TI's technique is working on a Truecrypt container mounted as drive. At least not for me. So files on such a drive that are in use during backup will cause an error.
Alex