Drive Snapshot differentials issue

Discussion in 'backup, imaging & disk mgmt' started by davidlynch, Dec 22, 2008.

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  1. davidlynch

    davidlynch Registered Member

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    With very little change on a system, the next differential snapshot backup results on big file(s). What could be the cause of it? is the backup really automagically skiping the swap file?

    Any help would be very appreciated.
     
  2. Aaron Here

    Aaron Here Registered Member

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    Windows XP or Vista?

    Between the time that you made the full backup and subsequent differential backup was the drive/partition degragged?
     
  3. davidlynch

    davidlynch Registered Member

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    XP. Yes, it was defragmented automatically with PerfectDisk Screen Saver schedule.

    Verified with another daily differentials and (unfortunately) defragmentation seems to be the problem.

    This behaviour is by default/design? no workaround?
     
  4. Brian K

    Brian K Imaging Specialist

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    davidlynch,

    I use PerfectDisk and defrag every month immediately prior to creating a new baseline image. My computer doesn't perform any differently before or after the defragmentation so I can't see any need to defrag more frequently. At the end of the month the diff images are around 5 to 6% of the baseline image size.
     
  5. Aaron Here

    Aaron Here Registered Member

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    David,

    By its intended purpose, defragging often moves files to different clusters/sectors. Any image backup program will see that as a change when it's asked to create an incremental or differential backup (though in actuality the files themselves probably haven't changed)!

    So if you believe frequent defragging results in improved performance (I for one don't think so) then you should stick with full backups.

    Aaron
     
    Last edited: Dec 23, 2008
  6. Brian K

    Brian K Imaging Specialist

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    I did tests on my mates computers with their co-operation. I did or didn't defrag their partitions while they were out of the house and asked them if their computers performed differently. Their answers were as good as tossing a coin.
     
  7. Aaron Here

    Aaron Here Registered Member

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    Brian,

    Same here... I used to be a defrag junkie, but eventually came to the realization that I didn't notice any performance improvement after running the defrag - so I kicked the habit. ;)

    Aaron
     
  8. markymoo

    markymoo Registered Member

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    My findings during a bout of testing, were taking an image added several minutes onto the backup time if i hadn't defragmentated in awhile which is like a week of heavy use. As a rule defragging cut down the backup time. I welcome to do your own tests. If you maintain your pc and keep the approx same amount of data each time you take an image. Take an image after defrag and one after a time and run a cleaner and you should see a bigger drop in backup time enough to convice you it worth to do the defrag before imaging. If you find an image taking a long time than usual you find it is momentarily pausing at certain stages as it slower on the reading or writing at those parts. It is also good to keep the drive you save the image to defragemented as well.

    It stand to reason if the drive arm has got to make big jumps across a big platter back and forth like crazy it going to affect the time not to mention wearing out your drive more. Hard drives have a higher transfer rate nowadays to cope with running XP much faster it less noticeable but over time if the pagefile becomes fragmentated there is a bigger dip in performance. High CPU resources also affect the time. It benefecial not to have anti-virus memory guards running or deep hooking software. Of course it all circumstantial to what your system is running. If the drive is very full or over 70% full that can slow it down so don't fill it up.
     
    Last edited: Dec 23, 2008
  9. Aaron Here

    Aaron Here Registered Member

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    My point was that if one intends to make differential (or incremental) image backups, interim defragging of the drive or partition in question is not advisable - doing so will likely result in (unexpected) large images! If interim defragging is considered to be of value then it's best to just make full-image backups.

    Imho, the value of defragging, the frequency that it should be done, and the choice of a defragger are all topics of speculation and/or subjectivety. ;)
     
    Last edited: Dec 23, 2008
  10. Brian K

    Brian K Imaging Specialist

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    Aaron,

    I do the same. Defrag immediately prior to a baseline backup. And not in between baselines.

    I'd like to make one observation about apps. PerfectDisk (in my computers) defrags without leaving any free space in the data. Diskeeper leaves one or two large areas of free space. Up to a GB in size. Without reason, these areas of free space changed position every few days and the following diff image was large (changed sectors). The number of fragmented files hadn't decreased so a "secret" defrag hadn't run. I haven't seen anyone else report this phenomenon and I no longer use Diskeeper. Weird.
     
  11. Jo Ann

    Jo Ann Registered Member

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    I'll pop-in on this discussion to say that my findings (at home and at work) completely support Aaron's views. Furthermore, since I am a Rollback Rx user I have yet another reason to avoid defragging my system partition (while RB is installed). So I create differential image backups until I uninstall RB (monthly), at which time I cleanup my system partition and run a defrag with UD before reinstalling RB.
     
  12. davidlynch

    davidlynch Registered Member

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    Thanks to everyone. From now on, scheduling defragmentations prior to full backups.
     
  13. Aaron Here

    Aaron Here Registered Member

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    Good idea. ;)
     
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