Sure, RAID level were only here to have a approximative comparison. I've read about reed-solomon, that's a very neat algorithm. In my 4x nodes example, 3x replication won't be possible (not a multiple). I don't see any alternative to avoid the "shortcoming" of replication, except using disperse with redundancy 2. Which is sadly not possible for a unknown reason (because reed-solomon is totally flexible in theory, therefore I don't understand why it's not authorized in Gluster!) Any thoughts? On Tue, Feb 7, 2017 at 2:51 PM, Nag Pavan Chilakam <nchilaka@xxxxxxxxxx> wrote: > You can always go for x3(3 replica copies), to address your need which you have asked > EC volumes can be seen as raid for understanding purpose, but don't see it as an apple-to-apple comparison. > Raid4/6(mostly) relies on XOR'ing bits(so basic addition and subtraction), but EC involves a more complex algorithm(reed-solomon) > > > ----- Original Message ----- > From: "Olivier Lambert" <lambert.olivier@xxxxxxxxx> > To: "gluster-users" <gluster-users@xxxxxxxxxxx> > Sent: Tuesday, 7 February, 2017 6:46:37 PM > Subject: Remove an artificial limitation of disperse volume > > Hi everyone! > > I'm currently working on implementing Gluster on XenServer/Xen Orchestra. > > I want to expose some Gluster features (in the easiest possible way to > the user). > > Therefore, I want to expose only "distributed/replicated" and > "disperse" mode. From what I understand, they are working differently. > Let's take a simple example. > > Setup: 6x nodes with 1x 200GB disk each. > > * Disperse with redundancy 2 (4+2): I can lose **any 2 of all my > disks**. Total usable space is 800GB. It's a kind of RAID6 (or RAIDZ2) > * Distributed/replicated with replica 2: I can lose 2 disks **BUT** > not on the same "mirror". Total usable space is 600GB. It's a kind of > RAID10 > > So far, is it correct? > > My main point is that behavior is very different (pairing disks in > distributed/replicated and "shared" parity in disperse). > > Now, let's imagine something else. 4x nodes with 1x 200GB disk each. > > Why not having disperse with redundancy 2? It will be the same in > terms of storage space than distributed/replicated, **BUT** in > disperse I can lose any of 2 disks. In dist/rep, only if they are not > on the same "mirror". > > So far, I can't create a disperse volume if the redundancy level is > 50% or more the number of bricks. I know that perfs would be better in > dist/rep, but what if I prefer anyway to have disperse? > > Conclusion: would it be possible to have a "force" flag during > disperse volume creation even if redundancy is higher that 50%? > > > > Thanks! > > > > Olivier. > _______________________________________________ > Gluster-users mailing list > Gluster-users@xxxxxxxxxxx > http://lists.gluster.org/mailman/listinfo/gluster-users _______________________________________________ Gluster-users mailing list Gluster-users@xxxxxxxxxxx http://lists.gluster.org/mailman/listinfo/gluster-users
