Gluster users - Feb 2018 - Quorum in distributed-replicate volume

On Tue, Feb 27, 2018 at 03:20:25PM +0530, Karthik Subrahmanya
wrote:
> If you want to use the first two bricks as arbiter, then you need to be
> aware of the following things:
> - Your distribution count will be decreased to 2.
What's the significance of this?  I'm trying to find documentation on
distribution counts in gluster, but my google-fu is failing me.
> - Your data on the first subvol i.e., replica subvol - 1 will be
> unavailable till it is copied to the other subvols
> after removing the bricks from the cluster.
Hmm, ok.  I was sure I had seen a reference at some point to a command
for migrating data off bricks to prepare them for removal.

Is there an easy way to get a list of all files which are present on a
given brick, then, so that I can see which data would be unavailable
during this transfer?
> Since arbiter bricks need not be of same size as the data bricks, if you
> can configure three more arbiter bricks
> based on the guidelines in the doc [1], you can do it live and you will
> have the distribution count also unchanged.
I can probably find one or more machines with a few hundred GB free
which could be allocated for arbiter bricks if it would be sigificantly
simpler and safer than repurposing the existing bricks (and I'm getting
the impression that it probably would be).  Does it particularly matter
whether the arbiters are all on the same node or on three separate
nodes?

-- 
Dave Sherohman

On Tue, Feb 27, 2018 at 4:18 PM, Dave Sherohman <dave at sherohman.org>
wrote:
> On Tue, Feb 27, 2018 at 03:20:25PM +0530, Karthik Subrahmanya wrote:
> > If you want to use the first two bricks as arbiter, then you need to
be
> > aware of the following things:
> > - Your distribution count will be decreased to 2.
>
> What's the significance of this?  I'm trying to find documentation
on
> distribution counts in gluster, but my google-fu is failing me.
>
More distribution, better load balancing.
>
> > - Your data on the first subvol i.e., replica subvol - 1 will be
> > unavailable till it is copied to the other subvols
> > after removing the bricks from the cluster.
>
> Hmm, ok.  I was sure I had seen a reference at some point to a command
> for migrating data off bricks to prepare them for removal.
>
> Is there an easy way to get a list of all files which are present on a
> given brick, then, so that I can see which data would be unavailable
> during this transfer?
>
The easiest way is by doing "ls" on the back end brick.
>
> > Since arbiter bricks need not be of same size as the data bricks, if
you
> > can configure three more arbiter bricks
> > based on the guidelines in the doc [1], you can do it live and you
will
> > have the distribution count also unchanged.
>
> I can probably find one or more machines with a few hundred GB free
> which could be allocated for arbiter bricks if it would be sigificantly
> simpler and safer than repurposing the existing bricks (and I'm getting
> the impression that it probably would be).
Yes it is the simpler and safer way of doing that.
>   Does it particularly matter
> whether the arbiters are all on the same node or on three separate
> nodes?
>
 No it doesn't matter as long as the bricks of same replica subvol are not
on the same nodes.

Regards,
Karthik
>
> --
> Dave Sherohman
>
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On Tue, Feb 27, 2018 at 04:59:36PM +0530, Karthik Subrahmanya
wrote:
> > > Since arbiter bricks need not be of same size as the data bricks,
if you
> > > can configure three more arbiter bricks
> > > based on the guidelines in the doc [1], you can do it live and
you will
> > > have the distribution count also unchanged.
> >
> > I can probably find one or more machines with a few hundred GB free
> > which could be allocated for arbiter bricks if it would be
sigificantly
> > simpler and safer than repurposing the existing bricks (and I'm
getting
> > the impression that it probably would be).
> 
> Yes it is the simpler and safer way of doing that.
> 
> >   Does it particularly matter
> > whether the arbiters are all on the same node or on three separate
> > nodes?
> >
>  No it doesn't matter as long as the bricks of same replica subvol are
not
> on the same nodes.
OK, great.  So basically just install the gluster server on the new
node(s), do a peer probe to add them to the cluster, and then

gluster volume create palantir replica 3 arbiter 1 [saruman brick] [gandalf
brick] [arbiter 1] [azathoth brick] [yog-sothoth brick] [arbiter 2] [cthulhu
brick] [mordiggian brick] [arbiter 3]

Or is there more to it than that?

-- 
Dave Sherohman