Re: [Bacula-devel] checking the block checksum

[Kern S. <ke...@si...>]

On Thursday 28 May 2009 15:50:45 Ralf Gross wrote:
> Ralf Gross schrieb:
>
> 26-May 04:51 VU0EA003-sd JobId 12376: Ready to read from volume
>     "A00098L4" on device "ULTRIUM-TD4-D3" (/dev/ULTRIUM-TD4-D3).
> 26-May 04:51 VU0EA003-sd JobId 12376: Forward spacing Volume
>     "A00098L4" to file:block 0:1.
> 26-May 08:06 VU0EA003-sd JobId 12376: Error: block.c:318 Volume data
>     error at 721:4451!
> Block checksum mismatch in block=106863406 len=64512: calc=9a831670
> blk=594c2ab
>
>
> I just bextracted the content of volume A00098L4 to disk, no block
> checksum errors and all md5sums are identical with the ones on the
> file server.

The code that extracts the data in bextract is identical to the code in 
Bacula.  You may be giving different instructions depending on exactly how 
you are extracting.

>
> I know I'm a bit annoying at the moment, but I need to nail down this
> problem. The hardware vendor already swapped 2 drives, with no change.
> The btape tests are running successfully and the backups since nearly
> 2 years too.

Checksum errors *could* be due to a bug, but that seems pretty unlikely since 
the code has not changed for a very long time, and we should see it with 
other users.  The most frequent cause of such problems is bad tapes, and 
typically that shows up in Alert reports (depending on how new your hardware 
is the info will be more or less complete) or in the kernel log.

>
> Is there a way to tell bacula to continue if a block error occurs or
> to retry? 

I believe most the utility programs and the SD accept the -p option (or 
possibly -P) to proceed on errors.  See the doc.


> Or to check this single block with a cli tool? 

Btape can position anywhere on a volume and read any block.  You can also make 
it do a "Bacula" style read-only scan where it should check checksums.

>
> Ralf
>
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