> Awesome, so now we can finally have proper "add nodes as you go" > setups without having to rebalance etc. Sweet!
I hate to be Mr. Negativity, but as the author of that patch I think it behooves me to point out that things aren't quite that good yet. The patch doesn't remove the need for rebalancing; it just makes rebalancing do something more reasonable. Let's say that we had two bricks A and B, with 1TB each. They would each receive 50% of new files. Now we add brick C, with 2TB. * Until we rebalance, A and B each have 50% of the files. * If we rebalance *without the patch*, A/B/C will each have 33% of the files. That's too much for A and B, too little for C. * If we rebalance *with the patch*, A and B will each have 25% of the files, while C has 50%. In most cases (e.g. except where this might cause excessive network/memory load on C) this is a better result. The "no need to rebalance" feature, in which existing files are left alone but new files are preferentially directed toward new bricks, is not yet implemented. The basic mechanism is to assign new layouts based on each brick's *free* space instead of total space. That's pretty easy to do, but risks creating a new problem. If we continue to allocate more files to the newer bricks even after balance has been restored, then we'll start to overload the new bricks. To avoid this, we need to do two things. (1) Periodically re-evaluate the divergence between our current layout and our ideal, setting a flag when the divergence is too great. (2) In the create path, if the flag is set, fix the parent directory layout before creating the new file. (Note for future implementers: instead of a flag, we could use the same "commit hash" technique as in http://review.gluster.org/#/c/7702/) As should be clear by now, this will not be a trivial addition. I think it still can - and should - be done for 3.7, but it's not there yet. _______________________________________________ Gluster-devel mailing list Gluster-devel@gluster.org http://supercolony.gluster.org/mailman/listinfo/gluster-devel
