Lars Marowsky-Bree <lmb@xxxxxxx> wrote:
On 2005-03-18T13:52:54, "Peter T. Breuer" <ptb@xxxxxxxxxxxxxx> wrote:
The problem is for multi-nodes, both sides have their own bitmap. When a split scenario occurs,
Here I think you mean that both nodes go their independent ways, due to somebody tripping over the network cables, or whatever.
Yes, or just a failover, where the active system crashes or is taken down (while the bitmap is dirty).
and both sides begin modifying the data, that bitmap needs to be merged before resync, or else we risk 'forgetting' that one side dirtied a block.
Right. And eventually we'd like to have that capability (of recombining bitmaps).
Could you set out the scenario very exactly, please, for those of us at the back of the class :-). I simply don't see it. I'm not saying it's not there to be seen, but that I have been unable to build a mental image of the situation from the description :(.
Typically, in a cluster environment, you set up a raid1 with a local disk and an nbd (or one of its variants) below it:
[raid1] / \ [disk] [nbd] ---------> other system
The situation he's talking about is, as you put it "somebody tripping over the network cables".
In that case, you'll end up with this:
system A system B [raid1] [raid1] / \ / \ [disk] [XXX] [disk] [XXX]
Where there's a degraded raid1 writing only to the local disk on each system (and a dirty bitmap on both sides).
The solution is to combine the bitmaps and resync in one direction or the other. Otherwise, you've got to do a full resync...
-- Paul - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
