Does Acronis Verify Disk Clone?

Discussion in 'Acronis True Image Product Line' started by incredidome, Nov 1, 2006.

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  1. incredidome

    incredidome Registered Member

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    To get it out of the way, I am paranoid and like to be sure without any doubt that my new drive is identical to the old. Acronis, which could be a faultless program, should never rely on the hardware writing correctly to the new disk or reading correctly from the old. "Crosstalk" and a number of other errors in transmission can occur.

    To start:

    I cloned my system disk using True Image 10's "Automatic" mode under "Clone Disk". Then I stepped away for the day and when I returned the clone was successful.

    Was the cloned disk compared to the original disk to verify the bits?

    If so, what technique was used: bit by bit or a CRC32 checksum/hash?

    My reason for suspicion:

    There was no option to verify the clone on "Clone Disk." According to the manual, this is only available in backup archive creation. Considering the manual says this preset is Disabled, I am led to believe Acronis does not verify the Clone automatically since verification doesn't seem to be standard.

    Also, "Operation 3 of 3" of the Clone Disk summary was "Copy MBR". There was no verification operation, so I know that the data was not verified AFTER everything was written.

    My theory:

    My theory, and please correct me, is that Acronis does not explicitly do any verification AFTER the cloning is complete. Instead, the inherit function of the hard disks confirms transmission WHILE everything is being written.

    According to http://www.dataclinic.co.uk/hard-disk-crc.htm:

    There are 156,296,385 sectors on my new 75GB disk. Sectors are split into 514 bytes. Sectors are the smallest area files are written to on the disk. 2 of the bytes are reserved for a CRC checksum that evaluates the sector, and if the remainder is 0 the data is correct but if not 0 there is an error.

    Because of this, Acronis may not explicitly verify the data, but the drives do automatically. When data from disk source is transferred to disk clone, since Acronis does the clone in sector-by-sector mode once the data is cloned the 2 sector's 2 byte checksums are compared and both must equal 0.

    While this sounds great, according to http://www.ciphersbyritter.com/ARTS/CRCMYST.HTM, CRC can only detect 99.998 of all possible errors.

    That means I have 156,296,385 sectors, 512 data bytes each, I am looking at a possible 3126 bytes that may be incorrect.

    So even if Acronis relies on the error correction functions of the disks alone, the clone can still be imperfect.

    In summary:

    Exactly how does Acronis or the disks verify the cloning operation??

    Thanks.
     
  2. incredidome

    incredidome Registered Member

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    No one wants to read that whole thing :D

    I just need to know... how can I be sure the clone is identical to the source?
     
  3. Xpilot

    Xpilot Registered Member

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    I am not sure that your warning voices are directing you in the right direction. For a start you could use imaging and restores. Programmed validations can be run at several stages in addittion to the built in checks if that would make you more comfortable.

    I believe there is more to concern you in the hardware than in one piece of software. You have mentioned CRCs in respect of hard drives. Without these checks and the ability to retry at allow level modern hard drives would not exist because small signal levels and packing densities errors need to be corrected.
    Now what sort of RAM do you have on your machine and does your computer support ECC ? see this extract from a memory company.
    Quote Do I need error checking?
    Most desktop computers take what's called "non-parity" memory and do not need error correction code (ECC), or "parity" modules. (However, in most cases ECC modules will work in desktops.) ECC modules look for errors in data and are most often found in servers and other mission-critical applications used by large networks and businesses. There are, however, a few desktop systems that do use ECC modules. In any case, you should buy the type of memory that's already installed in your system. You can tell which kind you have by looking at one of the modules currently installed. Count the RAM chips on one module. If the number of chips can be evenly divided by three or five, you should buy ECC or parity (whichever is offered for your system). If not, you should buy non-parity. For example, if one of your modules has nine RAM chips, you should buy ECC or parity. If one of your modules has eight RAM chips, you should buy non-parity. End quote.

    Now every time you switch on your computer let alone run a program random fluctuations in electronic system happen. Most will be insignificant others will be detected and corrected but there is tiny chance that some may make unwanted changes.

    Whatever you do keep a weather eye open on the progress of the next Solar Flare that is heading our direction so that you can shut down your system in good time.
    A UPS and a room sized Faraday cage would provide a measure of protection but low energy Cosmic Rays are another kettle of fish. [​IMG]


    Xpilot
     
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