[DRBD-user] a Newbie's Questions

Lars Ellenberg Lars.Ellenberg at linbit.com
Mon Oct 24 10:35:34 CEST 2005

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


/ 2005-10-23 20:53:52 -0600
\ Corey Edwards:
> On Mon, 2005-10-24 at 05:08 +0300, Louai Al-Awami wrote:
> > I am new to DRBD and have some  questions.
> 
> Welcome!

Thanks, Corey.
A couple of additional comments:

> >      1. Is DRBD used only to synchronize the whole disk? Can not I
> >         used to synchronize directories instead?
> 
> DRBD mirrors a block device. It knows nothing about files and
> directories, just the raw block data that is used to represent them. So
> the answer is no, you can't synchronize a directory. But, you can create
> multiple partitions and synchronize those. So instead of one partition
> at /home you could have /home/user1, /home/user2, /home/user3, etc. That
> of course would have its own set of ramifications which you would
> certain want to consider. LVM may also help you.

there are also symlinks.
so, you can have one or two drbds, then move the data directories
of your services there, and put symlinks in place...
(e.g. ln -s /mnt/ha0/var_lib_mysql /var/lib/mysql ... )

> > And can I use a meta-disk that is

you could (its just a define), but you'd break compatibility with upgrades.
and there might be unknown implications... so better not do that.
if you really need it (e.g. you want to use it in embeded devices),
ask for support at office at linbit.com, we'll explain the details ...

if you feel confident, and you know what you are doing, and you know
exactly that you will ever only use 1MB of the meta data, and you
understand the internals (how much meta data is needed for your storage
size), you can "fake" a larger block device using device mapper...
you probably don't want to do that either, too much hassle and to many
opportunities to shoot yourself.

cheers,

-- 
: Lars Ellenberg                                  Tel +43-1-8178292-0  :
: LINBIT Information Technologies GmbH            Fax +43-1-8178292-82 :
: Schoenbrunner Str. 244, A-1120 Vienna/Europe   http://www.linbit.com :
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