[DRBD-user] moving to a different backing device

Lionel Sausin ls at numerigraphe.com
Thu Feb 20 09:35:25 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.

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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