Re: [DRIVER SUBMISSION] DRBD wants to go mainline

[Lars Ellenberg <lars.ellenberg@linbit.com>]

On Sun, Jul 22, 2007 at 11:06:59AM +0200, Jan Engelhardt wrote:
> 
> On Jul 22 2007 00:43, Lars Ellenberg wrote:
> >On Sat, Jul 21, 2007 at 11:17:43PM +0200, Jan Engelhardt wrote:
> >> On Jul 21 2007 22:38, Lars Ellenberg wrote:
> >> >
> >> >We implement shared-disk semantics in a shared-nothing cluster.
> >> 
> >> If nothing is shared, the disk is not shared, but got shared-disk
> >> semantics? A little confusing.
> >
> >Think of it as RAID1 over TCP.
> 
> And what does it do better than raid1-over-NBD? (Which is already N-disk,
> and, logically, seems to support cluster filesystems)

DRBD has built-in logic
to track which copy of the data is the most recent.
DRBD has resource-level-fencing in place (though we can improve on that).
DRBD deals with concurrent writes of the participating nodes correctly.

"N-disk" is not the question,
you can stack drbd on top of md, lvm, anything.
N-nodes is the interessting thing.

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