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Re: [Bacula-devel] Backup Corruption with Certain Types of Drive


On Dec 7, 2008, at 5:20 PM, Allan Black wrote:

> Hi, all,
>
> After noticing a curious warning message from a catalog backup, I have
> been doing a little investigation and I now think that, with certain
> types of drive, a backup which spans more than one tape can corrupt  
> the
> data being written at the point where the tape change takes place.
>
> When a tape reaches the end of medium, there are two ways in which the
> drive may act:
>
> 1) The drive writes until it hits the end of the tape, i.e. the write
>  fails because the drive cannot pull any more tape past the heads.
>  In this case the write does not take place, and an EOM sense code
>  is returned.
>
> 2) The drive detects *impending* end of medium. In this case, the
>  write takes place, but an EOM is still returned.
>
> In case 1, everything is fine, and the backup proceeds as expected  
> (DLT
> and LTO both appear to behave in this way). In case 2, however, the  
> same
> data appears to be written twice: as the last block of the first tape,
> and then again as the first block of the second.


What OS is this?

There was a problem, a few years back, but since solved, with  
FreeBSD's pthreads.  It would cause data to be "written" to the end of  
the tape, but it would not actually reach the tape.

  http://mlblog.osdir.com/os.freebsd.devel.scsi/2003-06/msg00018.shtml

What OS are you running?

What version of Bacula?

What is in your bacula-sd.conf file?

-- 
Dan Langille
http://langille.org/




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