[DRBD-user] drbd upon md or md upon multiple drbds?

Lars Ellenberg Lars.Ellenberg at linbit.com
Thu Jul 7 12:01:46 CEST 2005


/ 2005-07-06 09:08:03 -0600
\ Corey Edwards:
> On Wed, 2005-07-06 at 18:46 +0400, Eugene Crosser wrote:
> > The subject says it all.
> > 
> > We got a couple of machines with 6 disks in each, on "dumb" SATA
> > controllers.  I would build md devices, and run drbd on top of them,
> > because md can "autorun" at boot time, so it seems more straightforward.
> >  But maybe there are some obscure reasons to do the other way around?
> 
> From http://www.drbd.org/drbd-article.html
> 
>         You can stack DRBD on top of md, md on top of DRBD is nonsense,
>         however.
> 
> I think your intuition is pointing you in the right direction. DRBD on
> top of md is simple, but md on top of DRBD gains nothing but
> complexities.

"nonsense"
because the drbds would need to be always in Primary on the same host...
you could do that, meanwhile. but it is not recommended.

btw, if you just want to "stripe" or "linear" map the devices, use lvm
instead, and put drbd on top of some logical volume there.

if you want real software raid (1,5,10,whatever), then use md,
optionally put lvm on top of the md, put drbd on top of md or lvm,
and if you really want to, you could then use the drbds as "pv"s in an
upper volume group. (the latter is not exactly trivial, either...)

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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