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Date: Wed, 26 Feb 2014 14:55:27 +0100
From: Polytropon <freebsd@edvax.de>
To: Matthias Apitz <guru@unixarea.de>
Subject: Re: errors from external USB disk
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On Wed, 26 Feb 2014 13:17:14 +0100, Matthias Apitz wrote:
> Sometimes, after the dump finished, a re-read of the file to get the MD5
> checksum results in errors and I was highly concerned about the integrity
> of my dumps on this device.

What error? Can you post the error message and the command
which caused it?



> I bought another 2.5 TB disk and was able to copy all the files (around
> 1TB) over, i.e. the device could now be owerwritte while testing.
> 
> What is the best way to run a test on the disk? I'm thinking in
> something like reading/writing the block in place for many days
> (it's around 1.5 TB). Any ideas?

You can start by looking at the S.M.A.R.T. data (sysutils/smartmontools
and sysutils/smartcontrol), see "man smartctl" for "smartctl -a".
This should help you to identify possible hardware errors.

If the disk is connected to USB, data _could_ be "lost" on that
way, too. Still it seems that your file system on disk is not
damaged (check with fsck -f /dev/da1s1a in umounted state).

The backup file should be entirely readable. You can copy or dd
it to /dev/null to make sure the entire file is being read.

Providing error messages could help to diagnose this further.
At the moment I'm just guessing. :-)


-- 
Polytropon
Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...