Differential backup question

Discussion in 'Acronis True Image Product Line' started by Shmuel, Feb 9, 2007.

Thread Status:
Not open for further replies.
  1. Shmuel

    Shmuel Registered Member

    Joined:
    Feb 9, 2007
    Posts:
    7
    Hi, I am new to this forum and a new user of this program. I have done a basic backup and followed it, after a week, by a differential backup. I understood that, as opposed to incremental backups, I'll have only one differential backup which will be substituted by the next differential backup each time.
    Now I have done a second differential backup and, to my surprise, the program added a new differential file: Mybackup 3.tib
    My question is what is then the advantage of a differential backup on the incremental, or... am I supposed to delete the Mybackup 2.tib after I have got the Mybackup 3.tib file?
    Thanks for your patience...
     
  2. MerlinAZ

    MerlinAZ Registered Member

    Joined:
    Aug 22, 2004
    Posts:
    91
    You can delete the 1st differential if you want.
    You will need to keep the full backup, and the latest differential.
    Just to be on the safe side, you may want to keep the prior differential.

    I usually do a full backup, then 3 incrementals, then repeat.
    I usually keep the last 2 full backups/incrememtals.
    That way I have a few restore points just in case.
     
  3. Shmuel

    Shmuel Registered Member

    Joined:
    Feb 9, 2007
    Posts:
    7
    Thank you, this IS helpful. So, what IS the difference between the incremental and differential? Say, if I have a PC at home full of data and programs, and I also have an external big HD for backup, which is the best way in order to backup all my HD, and be sure that I can restore all data if my HD stops functioning?
     
  4. seekforever

    seekforever Registered Member

    Joined:
    Oct 31, 2005
    Posts:
    4,751
    Both Incremental and Differential require a Full backup as a starting point.

    An incremental will backup all the changes made since the last backup whether it is the full or an incremental.

    A differential backup will backup all the changes made since the Full backup. It doesn't care that there are recent differentials.

    As an example, if you make a full and then make 100 changes your incremental will have the 100 changes and the first differential will have the 100 changes. You now make 1 more change and do a backup. The latest incremental will only have the 1 change, the latest differential will have 101 changes, the first 100 plus the latest 1.

    When you restore an incremental you have to restore the full and every incremental in the chain to get to the latest state. To do the same with a differential you have to restore the Full and only the last differential backup. So usually the incremental is faster to create but the differential is faster to restore.

    While you only need the full and the last differential to restore your system, TI9 required that you had to have all of the intermediate differentials to validate the archive. I can't remember if this bug still persists in TI10.

    Another slight weakness in the incremental method is that if you have a bad incremental in the chain you cannot restore any incrementals that were made after the bad one.

    You have to decide how important your data is and how you want to back it up. I find that backing up my OS really only needs to be done once in a while when I have made a change. I am able to restore everything since I have the files and CDs. To me, the important data is what I created myself like pictures, spreadsheets, letters and I spend more effort backing them up because if I lose them they are gone forever.

    You can read my basic backup philosophy in 3 posts within this thread:
    https://www.wilderssecurity.com/showthread.php?t=164672
     
  5. Shmuel

    Shmuel Registered Member

    Joined:
    Feb 9, 2007
    Posts:
    7
    Thanks, now it is much clearer. Yet, if you say that TI 9 has a bug, and you need to keep all the differential files you have ever made... it renders the whole differential system invalid. In one year I'll probably need 10 HDs in order to contain all these differential files :oops:
    Unless.. um.. I'll periodically delete all the tib files, make a new basic complete backup and start over again...?
    BTW, it is likely that Acronis came up with a patch or something to repair this bug, as it seems to me a basic issue and essential to the functioning of this program.
     
  6. seekforever

    seekforever Registered Member

    Joined:
    Oct 31, 2005
    Posts:
    4,751
    Well, not totally invalid since you can restore but without being able to validate the risk level is higher.

    IMO, you should never do long chains of incrementals or even keep doing a differential backup over an over without doing a new full at some suitable interval. It should work but it is asking for trouble.

    My basic plan would be to do a full on Sunday and incrementals or differentials for the rest of the week or if that seems like too much then make a full every second week. It is up to you. Then keep at least the last 3 backup/diff/incr sets and you should be well covered.

    I agree the differential validating flaw should be fixed but I didn't upgrade to TI10 so I don't know if they did in that release.
     
  7. Brian K

    Brian K Imaging Specialist

    Joined:
    Jan 28, 2005
    Posts:
    8,644
    Location:
    NSW, Australia
    seekforever,

    Could I ask about the sizes of your incremental files? I know they vary but what sort of range are you seeing as a % of the baseline image size. Do you find defragging makes much difference to the incremental size?

    It seems the only people here who discuss incrementals are those who don't like the process.
     
  8. seekforever

    seekforever Registered Member

    Joined:
    Oct 31, 2005
    Posts:
    4,751
    Sorry but I am one of the people who don't do them. The short answer is that it depends on how much your disk has changed. I don't have anything against doing a few after a full but the way I work only imaging my C drive when I think it is a good idea, just doesn't make incrementals worth the bother. My compressed images are 5-7GB so I just let them accumulate on my second HD. My data files are not imaged.

    Imaging programs do not look at archive bits or dates or whatever to determine what to backup when doing an incremental or differential image. They have a map of in-use sectors and then determine by comparing the maps what has changed. This seemingly bit of trivia gets us to your question about defragging. Yes, defragging can make a huge difference because even though the file contents are the same the fact that the data has been moved to other locations looks like a change to the imaging program which causes the sectors to be backed up. Note that changes on your C drive are not only what you do but various things Windows might write to record/optomize.

    You should defrag before making a full image and don't do it again until you are ready to do your next full image. An incremental of a defragged disk can be as large as the full!

    Edit, just remembered: If you have System Restore enabled it can by default use up to about 12% of your partition size for restore points. These keep getting added until the allocated space is filled.
     
    Last edited: Feb 9, 2007
  9. Brian K

    Brian K Imaging Specialist

    Joined:
    Jan 28, 2005
    Posts:
    8,644
    Location:
    NSW, Australia
    seekforever, our overall backup strategies are almost identical. I run different backup imaging software on different computers and I don't do incrementals with my TI computer. I do incrementals on another computer and my incremental sizes are 2% without defrag and 3% if I use daily defrag. I don't have System Restore enabled.

    One interesting finding was using Diskeeper as the defrag program resulted in much larger incrementals than using PerfectDisk. This was related to Diskeeper not being as efficient at removing free space between data blocks. When I looked at the Diskeeper graphic there was always a few GB of free space towards the centre of my C: drive. This free space sometimes increased or decreased in size "spontaneously" in the absence of a defragmentation being performed. I mean the data block after the free space was being moved. Whenever this happened the next incremental was larger than the preceding ones. This happened on all my computers running Diskeeper. I have no idea why this data block moved a few times a week.
     
Thread Status:
Not open for further replies.