Differential Backup - Deleted Files

Nope, use differential #1. In order to recover a deleted file, you have to restore the most recent backup made *before* the file delete.

A differential backup archives changes since the last full. Since the file delete happened after differential #1, that file delete is part of the delta that gets applied to differential #2.

Hello John and Garry,

Let me comment this situation.

Garry, thank you for the correct answer! That's correct that differential backup archives changes since the last full backup. 

John, in this situation you should restore the last backup which was made with non deleted file, as it was correctly suggested before.

In general, please keep in mind the difference between full, incremental and differential backups:

A full backup contains all data at the moment of backup creation. It forms a base for further incremental or differential backup or is used as a standalone archive.  A full backup has the shortest restore time as compared to incremental or differential ones.

An incremental backup file only contains data changed since the last full or incremental backup creation. Therefore, it is smaller and takes less time to create, but as it doesn’t contain all data; all the previous incremental backups and the initial full backup are required for restoration. To restore an incremental image, the incremental image and full image must be in the same folder.

Unlike incremental backup, when every backup procedure creates the next file in a “chain,” a differential backup creates an independent file, containing all changes since the last full backup. Generally, a differential backup will be restored faster than an incremental one, as it does not have to process through a long chain of previous backups.

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Thank you.

Hi Alexander

On a related topic, I was surprised to find that if I deleted an intermediate differential backup, any later onces cannot be validated (or mounted if they are partition backups).

I.E

Monday - Full
Tuesday - Differential
Wednesday - Differential

Delete Tuesday backup, and Wednesday backup won't validate or mount.

Why is this? Wednesday's differential backup should contain all the info it needs as long as the full backup from Monday exists? Is this how it's supposed to work?

Actually restoring the Wednesday backup seems to work fine.

Dave.

Edit: Typo

Just checked, and have found mounting works fine under the circumstances above - my mistake.

What I meant to say was that "exploring" the backup (by double-clicking on the Wednesday differential backup file in the above example) doesn't work. It asks for the missing Tuesday backup.

The validation issue above stands as described.

Dave.

Can anyone comment on this? I'd really like to know if this is the expected behaviour.

Dave.

Hello David,

Sorry for the delayed response.

We haven't faced an issue when particular differential backup deletion causes validation \ explore errors, because differential backup is not depended on any other backup in a chain except the full backup.

We will forward this situation to our QA team for reproducing, so could you please kindly provide me with the exact test case (exact steps to reproduce)?

Also, please do the following on your PC (where you're going to reproduce the issue): 

- Download the file;
- Run the downloaded file
The gathered information will be put in adv_report.zip in the same folder, where the AcronisInfo was saved.
Running AcronisInfo may take up to 5 minutes.

Then submit a request for technical support. Attach all the collected files and information to your request along with the step-by-step description of the actions taken before the issue appears and the link to this thread. Then please provide me with the case number you receive from our system, so I can pick it up and speed up the process. We will do our best to investigate the problem and provide you with a solution.

We are looking forward to hearing back from you at your earliest convenience.

Thank you.

Hi Alexander

Thanks for replying.

Not really sure how to log a request for technical support without having to pay, and I simply won't do that!

The problem is very easy to reproduce on my system. I have several Differential schedules, one to image the system drive and the others to backup data. Each runs daily.

As an example of the problem, I will describe what happens in the case of one of these backup sets - a directory containing 7 files, one full backup & 6 differential backup files, let's call them file1 (the full backup) and file2 - 7 (the differential backups, file7 is the newest file). This particular set is a data (rather than partition) backup. I am working through the actions as I describe them and the results below.

1) Validate file6 - the validation completes successfully.

2) Copy file4 elsewhere ( I used a different disk) and then delete the original file so that it is no longer in the same directory.

3) Repeat the validation of file6 - At the end of the job, it issues a request "Specify the location of volume 4" and offers me a choice of Browse, Retry or Cancel. When I click Cancel, the job fails.

4) From Windows Explorer, double-click on file6 (or file5) - A browse window pops up with a heading "Please locate volume number 4". After cancelling out of that, it is not possible to browse the contents of the file6 archive.

5) Perform a restore based on file6 (I restored to a new location) - Worked OK.

6) Copy file4 back to the original directory & repeat steps (3) & (4) - Both work fine.

My point is that neither validation nor exploring a differential backup should rely on the presence of any other differential backups, so the behavious in steps (3) & (4) is anomalous.

I am using ATI Home 2009. I believe I have provided sufficient information for you to be able to:

a) Reproduce the problem or deny that it exists.

b) Tell me whether this is fixed in ATI 2010.

Dave.

Edit: Typo & formatting