Incremental sector backup?

Discussion in 'Acronis True Image Product Line' started by ivar, Jan 23, 2005.

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  1. ivar

    ivar Registered Member

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    Hello!

    I have not clear how Acronis TI8 implements this? Where it stores information
    about changed sectors? And what happened when I make some changes into
    partition while operating-system is not loaded? Then TI8 probably never find
    out that changes are made into partition. Example I make some canges into
    partition OS offline, example change 10 sectors. Then makes some changes
    OS online, example 4 sectors into the same area. TI8 then only knows about those 4 sectors change. Now I make incremental backup and only 4 sectors
    of 10 are backuped. When I restore partition, then 4 sectors of 10 are restored correctly, but 6 sectors restored from old bacup-set. Those 10 sectors all must be one unit but after restore it isnt anymore. Relationship between those 4 and 6 sectors are broken - this becomes serious filesystem inconsistency. Wow about this ?

    Ivar.
     
  2. Acronis Support

    Acronis Support Acronis Support Staff

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    Hello Ivar,

    Thank you for your interest in Acronis True Image (http://www.acronis.com/homecomputing/products/trueimage/).

    Please note that Acronis True Image works independently of the operating system. Thus you may create images after booting from Acronis Bootable CD as well as under Windows. When you create incremental image Acronis True Image compares each sector with the full back up (or previous incremental) and decides whether it has changed or not. This process is the same under any operating system.

    If you still have any questions concerning the incremental images please feel free to ask here or by e-mail support@acronis.com.

    Thank you.
    --
    Ilya Toytman
     
    Last edited: Jan 24, 2005
  3. ivar

    ivar Registered Member

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    This is amazing......if I understand you correctly. You say that TI compares
    every single sector in partition with previous backup-set. Im confused.
    Example, if I have 200GB hdd......it reads it hours (comparison also) and if backup-set resides in the same physical harddrive as backed up partition, then reading time is doubled. Probably TI dont do this because I know that sector-based incremental backup is very fast, requires only seconds or few minutest and is mutch more faster than file-based incremental backup. It cant compare all single sectors. Where is the secret ?

    Ivar.
     
  4. Acronis Support

    Acronis Support Acronis Support Staff

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    Hello Ivar,

    The time for incremental image is less than for the full one because usually there are sectors that were not changed and Acronis True Image doesn't include them into image. Also please note that only sector which are used are being backed up. So it is not that long. And of course, the image creation speed depends on the performance of your system as well.

    Thank you.
    --
    Ilya Toytman
     
    Last edited: Jan 24, 2005
  5. ivar

    ivar Registered Member

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    But how TI find out what sectors are changed and what not?


    Ivar.
     
  6. Acronis Support

    Acronis Support Acronis Support Staff

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    Hello Ivar,

    Acronis True Image creates the checksum for each sector and then compares these checksums. The time needed to do it is very little.

    Thank you.
    --
    Ilya Toytman
     
  7. ivar

    ivar Registered Member

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    So, it makes checksum of every sector - it OK. Then it reads every sector in
    source partition, computes checksm and verifies it with previously saved
    checksums. Where TI saves this checksum, it is analog to catalog-file in
    file-based backup systems and their users can manually choose its location.
    You say that this checksum comparison process is very fast. Example I have 200GB hdd. How fast this drive can be readed from beginning to end. Yes, I know about smartsector technique, but example I have partition full of data. This reading speed dont depend from Acronis, but it depends from physical limitations of nowadays hard drives. This can be 10 MB/s (CPU does also other jobs and therefore it is little lower than physical limit).
    How mutch time it reads then this 200GB drive:
    200GB x 1024 = 204800MB
    204800 / 10 = 20480 sec
    20480sec = 5,6 h

    .......so this is exactly 5,6 hours. Compared with file-based incremental backups, that compares only file attribute change and this procedure gives
    only about 5 seconds.

    I think TI cant read drive from beginning to end and you mess something.
    Also Symantec support answer me that their sector-based incremental backup software V2i dont compare sectors but rather monitor in real-time
    disk activity and saves changed sectors into bitmap. V2i and TrueImage are
    exactly identical products. Why, this is not interest me, but it you really are
    authors of this software then you must know how it works.
    Acronis documentation talk also about this bitmap.
    Where TI saves this bitmap? I need to know it because this imformation is very important from incremental backup creation point of view and I dont want to loose this information by accidentally deleting it by example virus
    or maybe I can insert OS-offline changeded cectors presentation bits into this bitmap and maybe I can even choose safe location for this information?
    But most important that I want to know is - can I make changes into my
    bacuped partition from DOS or from other computer, harddrive disconnected
    from my computer and inserted to other computer for example virus romoving
    purpose?


    Ivar.
     
    Last edited: Jan 23, 2005
  8. Acronis Support

    Acronis Support Acronis Support Staff

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    Hello Ivar,

    Thank you for taking your time to post here and for your great interest in Acronis True Image (http://www.acronis.com/homecomputing/products/trueimage/).

    Acronis True Image is a sector-based backup solution. Acronis True Image uses checksums in order to check the sectors for changes. Acronis True Image doesn't monitor chaged sectors when operating system is up and running, Acronis True Image doesn't create any bitmap of changed sectors. All the checksums for each sector are stored in the image file.

    After creating the first full backup you can do what you want with the partitions you have imaged. The next incremental backup will include all the changes you made.

    The speed of the backup is a consequence of the unique snapshot technology developed inside Acronis company. This technology is the property of Acronis, Inc.

    Thank you.

    --
    Andrew Berezovsky
     
  9. ivar

    ivar Registered Member

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    Thank you for clear ansfer - that was all what was interest me.
    Its good news, now I dare to use it. I am surprised that TrueImage bases
    on independent technology. I know surely that Powerguest V2i Protector
    (now it is Symantec LiveState) dont compare changed sectors with checksums, it just monitors disk writes and sets bits to bitmaps. Of course
    this bitmap-based technology is very dangerous from filesystem consistency
    point of view. Imaginate what happened if operating system fails to insert
    bits into this bitmap - after restore partition contains some sectors with new
    data and others sectors with old data, and you can find out this no before
    than after restore. I was maked tests with V2i and all files those I was writing inside DOS, they all disapeared in incremental backups and never restored.

    Why Acronis dont advertise such important difference compared with its
    competitor-rival Symantec. Like me, I just fear to use TI before because
    I was fear to loose my filesystem. And I think many file-based backups users
    fear the same thing and therefore dont want to hear about sector-based
    backups.

    As I see now:
    What is positive in sector-based backups:
    1) faster file copy (backup), isnt need to copy complete file but only part of
    it, also isnt need to search directory.
    2) small backup-set size
    3) never mistake in "file changed" status. (file-based backups can mistake)
    4) saves one-to-one partition layout (if for any reason its important)
    5) low price

    What is negative in sector-based backups:
    1) very slow sectors comparison in incremental backups
    2) doesnt exist "system state" backup for domain controllers (zone
    replication etc)
    3) doesnt exist mounting-points
    4) doesnt exist databases backup support (from databases authors).


    Is this right?


    Regards,

    Ivar
     
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