[DRBD-user] drbd without a partition, for use with xen images

Lars Ellenberg lars.ellenberg at linbit.com
Fri Jul 25 12:37:29 CEST 2008

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


On Fri, Jul 25, 2008 at 11:49:33AM +0200, Heiko wrote:
> On Fri, Jul 25, 2008 at 11:07 AM, Robert Verspuy <robert at exa-omicron.nl> wrote:
> > Michael schreef:
> >>
> >> Why not to use loop?
> >> assing xen image to loop1 ( drbd1 (
> >> loop2 to drbd2 ... etc...
> >>
> Hello,
> 
> do you mean that I create a Xen Image, than do a "losetup /dev/loop1
> /VM/my.image"
> and than configure that loop1 as a disk:
> 
> on server1 {
>     device     /dev/drbd0;
>     disk       /dev/loop1
>     address    192.168.2.1:7788;
>     meta-disk  internal;
>   }

do not do this.
drbd on top of loop _will_ deadlock sooner or later.

you have been warned.

> or can I just do:
> 
> on server1 {
>     device     /dev/drbd0;
>     disk       /VM/my.image
>     address    192.168.2.1:7788;
>     meta-disk  internal;
>   }
> 
> 
> >
> > But then (I think), you can't do a live migration ??
> > because there's no software making sure that writes to the image from both
> > server do not write to the same block at the same time. (GFS does that)
> >
> > If you don't need live migration, you can use the loop, but when you want to
> > migrate (in a controlled manner, not failover), you have to do the following
> > steps:
> > - On Server A, stop Xen DomU
> > - On Server A, umount loop1 (drbd1)
> > - On Server A, set drbd1 from primary to secundairy
> > - On Server B, set drbd1 from secundairy to primary
> > - On Server B, mount loop1 (drbd1)
> > - On Server B, Start Xen VM.
> >
> we dont use live migration, for now.
> We just need a failover of the 1. VM goes offline we need the other
> one, with actuall data
> 
> I cant use a real partition because we have some VM on that machine
> that dont need drbd replication,
> also some are alone and others just do a mysql replication(inside the VM).
> 
> cheers
> 
> .rupertt
> 
> > Regards,
> > Robert
> >
> > --
> > *Exa-Omicron*
> > Patroonsweg 10
> > 3892 DB Zeewolde
> > Tel.: 088-OMICRON (66 427 66)
> > Fax: 088-66 427 69
> > http://www.exa-omicron.nl
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> >
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-- 
: Lars Ellenberg                           http://www.linbit.com :
: DRBD/HA support and consulting             sales at linbit.com :
: LINBIT Information Technologies GmbH      Tel +43-1-8178292-0  :
: Vivenotgasse 48, A-1120 Vienna/Europe     Fax +43-1-8178292-82 :
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