[DRBD-user] Replacing larger hard drives while keeping, services available?

Marco Prandini marco.prandini at ideafutura.com
Fri May 16 12:24:57 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.

Hello, I found this ML thread while preparing the same kind of
operation, I'd like to ask for a confirmation of what I think I learned,
since deviating from a recipe suggested by Lars Ellenberg makes me
uneasy :-)

He said:
> if you just replace the disks,
> you need to create new drbd meta data,
> and you need to do a drbd full sync.
> depends on the actual setup whether 
>  * full sync of local disk, then incremental sync of drbd,
>  * or just a full sync of drbd
> will be less efford.

so, let's suppose that waiting for a full sync is not a problem (since I
can't sync the new local disk from the old any way.

I'm planning to follow this procedure, that I already successfully
tested on a couple of virtual machines (steps marked with * are those I
have questions about):

1)  failover the services on server A
2)  replace the disk on server B
3*) restart drbd on server B, with the bigger local devices
4)  wait for A->B resync end
5)  transfer all the services on server B
6)  replace the disk on server A
7*) restart drbd on server A, with the bigger local devices
8)  wait for B->A resync end
9*) live grow the (etx3) filesystem on server B with resize2fs

First question: step 3 causes a full resync, that's ok for me, but
obviously drbd still reports the original size (constrained by A's
disk), however I suppose that the internal metadata in the new B's disk
is correctly allocated at the end of the bigger local device?

After step 7, as anticipated in the "Growing off-line" section of
drbd automagically recognizes the new device size, and performs another
full sync. However, the guide refers to the case when "the backing block
devices on both nodes are grown while DRBD is inactive". What I did is
not exactly the same. Do you see any risk with this procedure?

Would you suggest to "drbadm disconnect" server A before the step 9 , to
keep a copy of the data on server A's local disk in case there are
problems with resizing on server B?

Thank you very much for any comment.

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