Re: [Bacula-devel] Files autochanger

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

On Monday 23 August 2010 22:58:22 Radosław Korzeniewski wrote:
> W dniu 24 sierpnia 2010 00:35 użytkownik Kern Sibbald 
<ke...@si...>napisał:
> > > Yes, you are right. Bacula treats every Device as tape drive whatever
> > > it
> >
> > is
> >
> > > actually tape drive or hard disk.
> >
> > Bacula does not treat every device like a tape drive -- it had disk I/O
> > before
> > it had tape I/O.
> >
> > > This means Bacula can execute only one job for every device because
> > > this
> >
> > is
> >
> > > a restriction of single tape drive.
> >
> > This has absolutely nothing to do with tape drives.  The restriction is
> > because Bacula has a single file descriptor per device, and with a single
> > descriptor, you can only do a single restore at a time.  To restore
> > multiple
> > files simultaneously from the same Volume you *must* have multiple file
> > descriptors or somehow multiplex a single file descriptor.
>
> You better know Bacula history then me :)
> I juts read a source  code and explain it in that way.

OK, that is fine, but when drawing conclusions about why something is how it 
is, it would be better (more correct) to just state how it works, which you 
have correctly identified, then ask why it is that way.

>
> > > My solution to this problem is to create "virtual autochanger", that
> > >
> > > > will have more than one Device and will be able to run more then one
> > > > restore job at the time, here is my configuration:
> >
> > You can run multiple restore jobs either with or without a virtual
> > autochanger -- Bacula handles multiple devices without treating them as
> > autochangers.  However, I don't believe you will be able to restore
> > multiple
> > files simultaneously from the same Volume.
>
> Absolutely, but every file device must have different archive device
> otherwise it will not work.

Within Unix, you can open the same file more than once -- you don't need 
two "archive" devices.  However, Bacula does not do that.

>
> > > Till now, there are two possible solutions: "virtual autochanger" with
> > > custom Changer Command or vtape device.
> >
> > The third solution is simpler -- just have multiple devices.
>
> With restriction above. You can't share volume between different devices.

I am not sure that Bacula's Volume management code will let you open the same 
Volume on two different devices -- at least not version 5.0.x, which is why I 
said that I am not sure what you are trying to do will work.  Perhaps I made 
an exception for reading Volumes so that it can be opened multiple times, but 
I don't remember doing so.

Kern