>>>>> On Wed, 20 Jan 2010 20:56:50 +0100, Michel Meyers said:
>
> Hello,
>
> Not sure if somebody on the users list can answer this, but with a
> fileset that has this:
>
> FileSet {
> Name = "Backup"
> Include {
> Options { signature=MD5; }
> ...
>
>
> 1. Where are the signatures actually generated?
On the FD.
> 2. Are the signatures checked when a restore is done?
No, I don't think so. That signature is only used by verify.
>
>
> I'm asking because I recently had a weird issue with Bacula and am
> wondering whether my diagnosis is correct.
>
> Backstory: I recently inherited an Exabyte 110L LTO2 Loader (IBM
> Ultrium-TD2 drive) and PCI-E SCSI Controller (Adaptec ASC-29320ALP
> U320). My storage 'server' doesn't have a PCI-E slot, so I hooked all
> this up to my newer 'desktop' PC and installed an SD there (both run
> Bacula 3.0.3 on Debian Testing with a 2.6.30 kernel). To test the setup
> I started a backup with a few bigger files (mostly CD images) from the
> server and then restored and compared them to the originals. The restore
> process didn't complain about the files but to my surprise, they didn't
> match. A closer inspection showed that all of the files only differed in
> a single byte.
>
> A few weeks later my desktop PC went haywire, which I eventually
> diagnosed as faulty memory (segfaults and gpfs in Linux and both
> memtest86+ and Windows Memory Diagnostic found issues with 3 of the 4
> RAM bars). Knowing that this PC has had sporadic issues previously (with
> Windows Vista dumping to blue screen and complaining about the RAM when
> it came back) I replaced all of the memory modules and figured I'd
> retest Bacula again. It turns out that this backup and restore worked
> flawlessly (same amount of files backed up and test files, but it did
> use a different tape than in the first test).
>
> Hence my question: How could the file difference slip past the restore
> process and is it possible that faulty memory on the SD can cause silent
> data corruption? Or is that not possible and the fault actually lies
> with either the tape, the drive or the controller/controller cable?
Yes, I think faulty memory on the SD could cause this. It could cause a whole
load of other things to go wrong too.
Blocks written to the volumes have their own checksums, which are checked when
the tape volume is read, so I think that problems there would be detected.
__Martin
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