Differential Backup Does Not Work
Ever since my upgrade to ATI 2016, I have had nothing but trouble performing differential backups. Attached is a screen shot of the latest headache. As you can see, on 12/26 a full backup was performed. For 5 days after that a differential was performed. As I'm sure you know, a differential backup always includes whatever changed files were backed up in the previous differential, so as the days progress the differential files grow in size, as you can see in the previous backup set started on 12/20. But the 12/26 set had a large differential on 12/27 (probably because it finally decided to backup my Outlook database, but that's another failure issue). However, on 12/28, the backup set shrank dramatically which a proper differential backup would never do. Anyone have any ideas as to what is going on? Are these kind of problems fixed in ATI 2017?
Thanks for your assistance.
Thanks for the feedback. Unfortunately i believe you have misread the photo. The 12/27 backup is of course a full backup - 469Mb. On 12/28, what you label as 1, the first differential backup is 518Kb. All good so far. However, the next differential on 12/29 is only 60Kb! This is the problem. The 12/29 differential MUST be at least as large as the previous backup. Thoughts?
518kb and 60kb are almost nothing - as the disk moves files around, it may be using different blocks on the disk to store the data.
Even if that's not the case, A differential can be smaller and there are a number of situations that can explain this. Remember, differentials are based upon the data in the full and not what's in each of the other differentials.
If you have file on Monday and take a differential backup, then delete that file and then the backup is run again, the next differential will be smaller because there is now less data on the drive to be backed up. This is more apparent when the file is large, but again, the difference of 518kb and 60kb is almost nothing, but it's quite possible that files were modified (making them smaller) or deleted - both of which could result in a smaller backup. Want to test this... copy your Acronis installer.iso to your desktop and run a differential. Now, delete the .iso and empty the recycle bin and then run another differential - the new differential will be smaller.
Running disk cleanup (this will cleanup up temporary directories, recycle bin, etc). If you click the system box this will also cleanup older Windows updates that would have been in the pervious backup (whereas temp files, recycle bin may not if they are in your exclusions).
Deleting files/folders from the user profile or anywhere else on the disk that is being backed up after one backup and before the next can result in a smaller backup size.
Modifying files/folders. For instance, you can have a 2Mb Word docuement on Monday, decide you don't like the last paragraph so you remove it and save the file (making it smaller) and then backup that change - this would be a smaller file than the previous day, which could result in smaller size backup.
Modifing software - some upgrades remove previous versions and install new versions which can be smaller. This can also remove older logs that have built up size over time.
Speaking of log files... they're everywhere and can be different sizes for a number of reasons. Many logs start clean with each Windows startup or user logon. Installer logs, Windows update logs, etc are constantly changing as well.
If you want to try and find the exact difference, the only suggestion I can provide is to mount differential 1 and differential 2 and then run an instance of treesize free agains each of the mounts and pick through the folders for different file sizes and see if you can pinpoint the exact difference.
I agree with Bobbo. As more days pass after the full backup, there will of course be more changes to the system. But, it doesn't follow that all changes result in larger disk use.
The size of the differential backup on 27 December is about 500meg, whereas all the others (includsing subsequent ones) are under 100meg. This suggests that something was added and then removed.
Is it possible that that one differential backup used sector-by-sector explaining the larger size? It does not make sense to me for that to happen, but just speculation on my part.
Ian
Defragmenting a drive can also cause wide differences in backup file sizes.
Thanks for all your input. There were no files removed, defragment does not run on this drive automatically, and this is a file backup not a sector backup. I don't see any way one could account for a 90% reduction in the differential backup file size. And Acronis is so slow to open a backup file that I don't have the time to search all the files in the 12/28 and 12/29 backups to see what is different. My experience so far with this release of Acronis has been very frustrating, not the least of which is its now failure to back up Outlook .pst files, when the files are not in use overnight when the computer running Outlook is shut down. Looks like i have to find another SW solution for my on-site backups.
What folder is your file/folder backup - your user profile? If so, again, there are numerous logs and directories in the hidden appdata folders that can increase OR DECREASE with logins, changes to the system (every time you reboot or logon there are changes being made), applications etc. Logs are a big one, but there are lots of things in appdata folders that change on a daily basis, pst's, iTunes databases, iTunes backups, logs, other application databases, etc. Other tools like dropbox, onedrive, etc that synch with other folders can also cause changes in a directory that is being backed up that would result in smaller size.
Regardless of what backup software you use - this behavior will not be different for you if something changed on the disk that resulted in a smaller size on disk. If you don't want to investigate, that's fine, but you're not doing yourself any favors as you have the data and the suggested tools to validate this yourself. No one else can do it, but you. I've had this conversation many times in the forum, and sure enough, after comparing, the cause was identified.
If you mount two differentials and use foldersize free to compare them and pinpoint the size change to a folder or file, you'll know exactly where the difference occured. I guarantee you that Acronis did not delete or miss something between the backups, but something was different on the disk at the time of those backups being taken.
The only files backed up by Acronis is the Documents file. I agree that some files may be changed by the OS, but I have used Acronis for years and only with this new release have I seen this behavior where there is a 90% reduction in the differential file size.
I get that, I really do, but something changed on the disk - in that directory - 100% guaranteed.
You may have never seen this before, and perhaps maybe never will again based on when the backups run and what is in that directory at that time. But if you compare the two backups with treesize free, you'll be able to find out what file or folder had differences based on their size and that will help shed light as to what changed.
My documents has links to My Music, My Pictures, My videos - files could have been changed there - especially if using iTunes or some other media program that has a database and/or log files. Many apps also put folders in my documents with logs or for ouputting data.... (I have a folder from AnyVideoConverter that contains logs and is the default location for when I convert video files, I have an Audible directory that was created that has logs and contains the default location for Audible downloads, I have a hidden folder called "cache" with a left over empty "tempfile" folder that some application put there at one point and apparently deleted the files when it got done but left the folder behind. Outlook PST's are often created there by default and those can change in size as you cleanup your mail folders. ). This is normal stuff and can still relate in a smaller backup.
Unless you compare the sizes with Treesize, it will always remain a mystery, but it is not hard to do this.