Message-ID: <1034063377.655.1711613387926.JavaMail.Confluence$@Confluence> Subject: Exported From Confluence MIME-Version: 1.0 Content-Type: multipart/related; boundary="----=_Part_654_1480673379.1711613387925" ------=_Part_654_1480673379.1711613387925 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Content-Location: file:///C:/exported.html Understanding Image Verification Failures

Understanding Image Verification Failures

Though they do happen, verification errors are extremely rare. W= e estimate that less than 1 in 1,000 systems have problems that lead to ima= ge file corruption. The vast majority of Macrium Reflect users will never e= ncounter a single verification issue.

This article explains what hap= pens during the image verification process and how to troubleshoot problems= with your system.


What is a verification failure?

Quite simply, it means that data that was written to the backup or image= file is not the same as is read back from the same file.

Errors of = this type are symptomatic of a computer system with a marginal hardware pro= blem. The most likely suspect is your backup media - but memory and motherb= oard faults can also cause this issue.

How does Macrium Reflect check the data integrity?

Data blocks read from the image file are compared with the original data= that was read from the image source disk by using a hash comparison. =

When an image is created each block of data (generally 64K but may be la= rger depending on the partition size) has an MD5 hash digest created after = it is read from the disk and before it is written to the image file= . This hash value is saved in the index of the image file. When th= e file is read back the hash value is recalculated and compared with the or= iginal hash in the index. Any discrepancy between the two values indicates = that the image file is corrupt or cannot be read back reliably.


Macrium Reflect uses the unmodified code from the reference implemen= tation of the RSA Data Security MD5 message-digest algorithm. This guarante= es that the same block of data cannot generate a different message digest (= hash) value. If data is read back with a different MD5 hash value to the va= lue that was generated when the data was originally read from disk, it is g= uaranteed to be corrupt. This is always outside of the control of Macrium R= eflect as the OS will report a write without any error.

Why can't Macrium Reflect validate the data as i= t is written?

It isn't possible to verify the file as it is written because the buffer= s and caches in the write process aren't flushed to disk until after the fi= le is closed. The only way to verify data integrity is to close the file at= the end of the backup process and then read the file back. It's possible t= o do this automatically by selecting the 'Auto-Verify' option in the Advanced backup definitio= n properties.

Why don't I have any other problems with my system?

You do, you just haven't noticed it yet. If your PC can't write and read= back data reliably then this won't just be a problem with Macrium Reflect,= all software on your PC will be vulnerable to same problem. Macrium Reflec= t is either the first to trigger  it or is the only software reporting= the problem to you.

Files are not checked for integrity by Windows,= so unless an application does it explicitly, disk errors could have been o= ccurring silently. Macrium Reflect handles very large volumes of data with = a consequently high chance of triggering any intermittent hardware errors.<= /p>

I don't believe you. How can I be s= ure it isn't a problem with Macrium Reflect?

To independently corroborate the problem you can use a third party utili= ty to show the same corruption:


Note: The DOS copy command and ExactFile check= s aren't conclusive as file checkers read the file sequentially and the err= or may only occur during random access. Due to the different execution and = data paths, success in any of the detail test is not an absolute guarantee = that your hardware is fault free.


Troubleshooting verification problems:

The key to resolving verification errors is to locate the source of the = corruption. This can be very difficult and may involve replacing PC compone= nts or upgrading firmware or software drivers.

1= . Isolate the backup drive

If the backup drive is an external drive then backup to the= same drive using a different PC. If your system is generally stab= le then the issue causing the verification error may have very low probabil= ity of occuring. Therefore, to optimise the chance of triggering it, you sh= ould try to backup the same or a greater volume of data. If you still recei= ve verification errors then your drive is faulty and you should use a diffe= rent backup device.

2. Use different data leads and ports

If possible try using a different sata or usb leads or connecting the de= vice to a different port. Also, if using USB, try removing any USB hubs bet= ween the storage device and the computer.

3. Try a different backup destination 

Try combinations USB/Fire-wire/eSata/Network. If you only get corruption= with one of the connection types then that sub-system has a problem. Updat= ing the firmware or software drivers for the controller might resolve the p= roblem.

Also, try connecting directly to a USB port with high a qua= lity USB cable. USB hubs can often be a source of corruption. = ;

3. Replace or swap out your RAM modules

If the error can't be traced to a single component then you may have fau= lty system RAM. If you have more than one RAM module installed then swappin= g out the memory can isolate the faulty RAM module.
Note: Memory checkers such as 'memtest86' will often fail to find any pro= blems even though there is a latent issue with the RAM.

4. Turn off your anti-virus software

We have had an uncorroborated report that some anti-virus software can c= orrupt disk writes. If you find that your images pass verification after di= sabling your AV software then we strongly recommend that you un-install you= r AV software as it is compromising your system.


See Also:
Verifying image and backup files
Verifying im= age and backup files from the command line 

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