[Gluster-users] Expand distributed replicated volume

[Anuradha Talur]

----- Original Message -----
> From: "Anuradha Talur" <atalur at redhat.com>
> To: "Gandalf Corvotempesta" <gandalf.corvotempesta at gmail.com>
> Cc: "gluster-users" <Gluster-users at gluster.org>
> Sent: Tuesday, July 12, 2016 1:16:00 PM
> Subject: Re: [Gluster-users] Expand distributed replicated volume
> 
> 
> 
> ----- Original Message -----
> > From: "Gandalf Corvotempesta" <gandalf.corvotempesta at gmail.com>
> > To: "Anuradha Talur" <atalur at redhat.com>
> > Cc: "gluster-users" <Gluster-users at gluster.org>
> > Sent: Thursday, July 7, 2016 10:14:46 PM
> > Subject: Re: [Gluster-users] Expand distributed replicated volume
> > 
> > Il 07 lug 2016 13:18, "Anuradha Talur" <atalur at redhat.com> ha scritto:
> > > Node to the cluster? You can add one per time.
> > >
> > > If you are asking about adding the number of bricks to a volume,
> > > in case of replica 3, if you want to keep the replica count same (3)
> > > then you have to add 3 bricks. These three bricks will be taken as a
> > > new replica group added to the volume.
> > >
> > > If you want to increase the replica count to 4, then you will have to
> > > add one brick each to all the existing replica groups. So that the
> > > replica groups now have 4 bricks each.
> > >
> > > Hope this resolves your query.
> > 
> > Lets assume a 3 nodes cluster,  replica 3, 6 1tb disks per node, 1 brick
> > per disk.
> > 
> > i would like to increase space and thus add a new node.
> > Can i add a single node with 3 disks/bricks and automatically rebalance?
> 
> Yes you can add single node with 3 bricks. But, given that you are keeping
> the replica count
> same, these three bricks will be replica of each other. It is not so useful
> in case of node
> failures/shutdown.
> 
> > In this case, gluster moves data around to use the maximum number or disks
> > for performance reasons?
> > 
> There are 2 ways to trigger rebalance after adding brick,
> 1) without force option : This will not move data. But will add linkto files.
> Think of them as symbolic links. Files will reside in the bricks where they
> already exist,
> but will have links in the new bricks.
> 2) With force option : This will actually move the data from old bricks to
> new bricks.
> 
> Both these operations will be done only for those files that need to
> be migrated.
> 
> The new files will either
> 1) be created in new bricks if they hash to new bricks.
> or
> 2) be created in new bricks even though they hash to old bricks and old
> bricks will
> have linkto files.
> 
> If there is no space in old bricks to create linkto files too, the operation
> will
> fail with ENOSPC (no space available).
> 
> I'm cc'ing developers from DHT team in case you have more questions with
> respect to
> rebalance.
Sorry for spam. Forgot to CC.
> > We start with 18tb raw, 18 disks, 6tb usable, 100% used (6tb on 6 usable
> > disks)
> > After adding the new node with 3 disks we will end with 7tb usable.
> > all disks would be used as 6tb/7=0.85% right?
> > 
> 
> --
> Thanks,
> Anuradha.
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> 

-- 
Thanks,
Anuradha.