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Re: [Bacula-devel] Couple questions about using a "disk-changer"


On Monday 18 August 2008 20:07:03 Joshua J. Kugler wrote:
> On Sunday 17 August 2008, Kern Sibbald said something like:
> > There is very little documentation for the disk_changer script,
> > because it was originally intended for testing, and is extensively
> > used in the Bacula regression scripts.  There is at least one very
> > large user that is using disk_changer in production ...
> >
> > The main place for "user" documentation on using the script is at the
> > top of the file.
>
> Yup, have read that.  Will read it again to try to internalize more of
> it.
>
> > Before using disk_changer to access a slot, you must create the slot
> > (sort of like inserting a blank tape).  Typically I do it by:
> >
> >   touch <disk-changer-directory>/slot<n>
> >
> > where <n> is the slot number you want to use.
>
> OK, thanks. That's what I assumed.  So basically, an empty file.  Cool.
>
> > By default, disk_changer allows a maximum of 10 slots, and two
> > drives.  The doc (at the top of the file) tells you how to modify it.
>
> Right.  If using S3, then basically you'd set your max to as many
> volumes that fill up the amount of space you want to pay for. :)
>
> > > 2. Is there a database independent way of getting information about
> > > volumes?
> >
> > list volume=xxx
> > or
> > llist volume=xxx
>
> OK, that requires piping to bconsole, which shouldn't be too bad.  Just
> wanted to avoid that if possible.

At the moment, it is probably the simplest option ...

>
> > or the equivalent SQL commands.
>
> Right, but that would require find the type of database, getting the
> passwords (which requires parsing the bacula config file if not
> SQLite), and then issuing a query once connected.  Bconsole might be my
> best route. :)
>
> > There is a C interface to the databases that is mostly SQL database
> > independent, but it is written only for Bacula so would not be easy
> > to use in an external program.
>
> Where might I find code (docs?) for that? 

<bacula-src>/src/cats  =>  code

Developer's doc has some old documentation of the database format.

> But that would still require 
> parsing, say, bconsole (for the director password) or the larger conf
> file for database passwords.  

Yes, though version 3.0.0 will probably have a much simplified way of getting 
the DB info.

> Is there any documentation on basically 
> creating one's own bconsole, such that you connect to the director and
> query directly?

The developers doc explains the comm protocol, but you pretty much need to 
read the console code ...

>
> > You can always use a DBI interface -- e.g. perl, or libdbi ...
>
> True.  And I guess for just getting info about the databases, the
> queries will be the same, no SQL differences needed.
>
> > I am a bit skeptical about the practical use of S3, but it is clearly
> > something we need.
>
> It would be cool, yup.
>
> > I believe the best way (maybe not the easiest) is to implement it as
> > a Bacula device driver in the trunk svn.  The trunk has a fairly well
> > defined interface to device drivers that make adding new ones more or
> > less trivial. For the moment it requires compiling it into Bacula,
> > but at some point we will have a plugin interface.  For the moment,
> > this interface is only documented by the code.
> >
> > Doing it via the disk_changer probably will not be possible since
> > accessing S3 with any degree of security and control requires
> > programming at the open, read, write, lseek, close levels via their
> > API.
>
> For the moment, I'm going to see what I can come up with via disk
> changer, since the systems I'll be using it on are only used for
> backup, with no other user logins, so there is no chance of the volumes
> being tampered with.  Doing direct opens/reads/writes would make the
> backup very slow.  My idea with disk changer is to have another process
> that handles uploading so the backup can proceded at full speed.  Like
> I said, it's in the idea stage...we'll see how far I get.

OK, good luck,

Kern

>
> j



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