[DRBD-user] moving to a different backing device

Wayne lists-drbd at useunix.net
Thu Feb 20 18:08:59 CET 2014

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


Thanks for the reply. Ok, I think I'll just start with the 'dd' route
and then do a resize once both systems are upgraded. So how does DRBD
keep track of the size of the backing device? Is that via the
/var/lib/drbd/drbd-minor-?.lkbd files?

I have backups but a resync adds a lot of I/O load to the Primary
server which is a very busy DB server which is why I'm trying to avoid
a resync.

I'll start with the 'dd' method and if that works I'll report my

Thanks again,

On Thu, Feb 20, 2014 at 09:35:25AM +0100, Lionel Sausin wrote:
> Dear Wayne,
> I'd expect DRBD to find the meta-data even if the backing device is 
> larger, because from DRBD's point of view, the resource's size does not 
> change until you run "drbdadm resize". So I'd say: you /should/ be fine.
> Now to be honest, you don't have to trust me, as I usually let DRBD do a 
> complete resync when I replace backing devices. Adaptive resync rate 
> keeps  the resource responsive, and I have backups if ever the 
> up-to-date node crashes in the meantime. I the end I treat it like a 
> RAID rebuild.
> Lionel Sausin.
> Le 20/02/2014 02:34, Wayne a écrit :
> >I currently have DRBD 8.3 working between 2 Debian boxes with external
> >RAID storage as the backing device. I intend to update the RAID storage
> >on each system since they are rather old now. I need to do this with
> >minimal down time of course. What is down-time ever maximal, LOL?
> >
> >The backing stores on each system right now are identically sized
> >logical block devices (LUNS) exposed by the RAID hardware.
> >
> >I've already installed one RAID onto the secondary DRBD system. My plan
> >is to take the secondary DRBD offline, use 'dd' to move the data from
> >the current RAID to the new RAID, reconfigure the backing device to the
> >new RAID and set DRBD online. I'm hoping this will only require a
> >re-sync of the blocks that have change since the secondary was brought
> >down.
> >
> >I believe a problem is that the new backing device is much larger than
> >the current backing device. So a straight dd won't place the meta-data in
> >the correct position on the new block device? Is this a correct
> >assumption? If so what is the correct way to handle this migration while
> >minimizing re-sync time?
> >
> >Is this even the correct approach? This is my first crack at this so I
> >may be way off.
> >
> >Any and all help is appreciated.
> >
> >Thanks,
> >Wayne
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> >drbd-user at lists.linbit.com
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