R: R: Network mirroring (was:R: Questions)

[Giampaolo Tomassoni]

> > A better fs-independent networked raid solution should be scalable, 
allowing
> > more than two hosts to cooperate in the creation of a 'virtual' raid. This
> GNBD allows more than one client.

It does. But needs to open a tcp connection between two nodes. I.e.: if you 
have 3 nodes among which you want create a raid1, you have to create a tcp conn 
between node 1 and 2, as well as between node 2 and 3.

Besides, this way if node 2 crashes, you miss a route to sync node 1 and 3 
toghether...


> But it suffers from consistency problems (at least this is what i figured
> out in my 1 min look at the code).

You mean at startup? Reading the sources, I had the feeling that a read and a 
write wouldn't be completed untill the mbd completed the tcp transaction with 
the remote node.


> > would be better implemented using (possibly multicast) udp messages. Here 
the
> > matter is complicated by the need to keep in sync every local image of the 
raid
> > (srv A writes and sends an update, srv B looses the update and wanna read), 
but
> > It should be made at the md or raidX layer in Linux, not below...
> Nod. I will send the RAID1 write-only patch tomorrow which at least makes
> the NBD+RAID1 more faster.

Nod? What does it mean 'nod'?


>   - Marcelo

Giampaolo,

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