[DRBD-user] Hard disk upgrade

[Lars Ellenberg]

/ 2004-01-29 16:47:55 +0100
\ matthias zeichmann:
> status quo is:
> machine atem holds all the ha services and all drbd devices in a sane
> state. [0]
> machine kaelte has been freshly rebuild with new (larger) disks. some
> drbd devices were partitioned to hold more diskspace [1]. drbd devices
> are formatted ext3 and hold no data.

Well, the sync will void the formatting. This part of it was
nonsense, unless you use plan B.

> Plan a:
> bring up drbd on machine kaelte without changing drbd.conf (disk-size
> still the same as on host atem)
> meaning fullsync  atem -> kaelte
> start heartbeat on host kaelte and let it assume its native services
> (disksize of drbd devices should be as always)
> stop heartbeat on host atem and let kaelte take over its services
> stop drbd on host atem (-> hard disk upgrade)
> 
> and now the critical point which might as well be impossible to work
> anyhow: change disk-size in drbd.conf to reflect the real disk-size of
> the devices and restart drbd on host kaelte. will this blow my
> machine/setup/cluster? 

plan C: hook up all disk in one box, an do
dd if=/dev/good/data of=/dev/new/disk, then move one half of the
disks to the other box.  its faster, you can skip two full syncs,
but you'll have a downtime.

plan A:
with minimal downtime I think it should work like this:
bring up kaelte 
	The disk-size parameter should already correspond to the
	real (new) device size.
	As long as device size is larger than fs size, fs does not care.
	On connect drbd will "agree" on the minimum of device sizes.
	wait for the sync atem -> kaelte
	start heartbeat (and thus services)
on atem stop heartbeat and services
on atem stop drbd
	hard disk upgrade
	config (disk-size) upgrade
	rm /var/lib/drbd/*

Now you _could_ just start drbd on atem, and it _should_ work.
I'd prefer to have a short downtime on kaelte first:
stop heartbeat and all services, restart drbd, restart heartbeat
and all services, just to be sure the bitmap and so on is
correctly allocated.
Then start drbd on atem, wait for the full sync kaelte -> atem,
start heartbeat and services ...

plan B:
of course you could just rsync it all over to the newly formatted
disks, not using drbd. You have to make sure you get a consistent
and uptodate view of your data.
Then first stop all on atem, second start all on kaelte,
Now upgrade atem.
Then start drbd on atem, wait for the full sync kaelte -> atem,
start heartbeat and services ...

hth,

	Lars Ellenberg