Gluster users - Mar 2017 - Node count constraints with EC?

Hello list.  Newbie question:  I?m building a low-performance/low-cost storage
service with a starting size of about 500TB, and want to use Gluster with
erasure coding.  I?m considering subvolumes of maybe 4+2, or 8+3 or 4.  I was
thinking I?d spread these over 4 nodes, and add single nodes over time, with
subvolumes rearranged over new nodes to maintain protection from whole node
failures.

However, reading through some RedHat-provided documentation, they seem to
suggest that node counts should be a multiple of 3, 6 or 12, depending on
subvolume config.  Is this actually a requirement, or is it only a suggestion
for best performance or something?

Can anyone comment on node count constraints with erasure coded subvolumes?

Thanks in advance for anyone?s reply,
Terry

_____________________________
Terry McGuire
Information Services and Technology (IST)
University of Alberta
Edmonton, Alberta, Canada  T6G 2H1
Phone:  780-492-9422

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Hi Terry, 

There is not constraint on number of nodes for erasure coded volumes. 
However, there are some suggestions to keep in mind. 

If you have 4+2 configuration, that means you can loose maximum 2 bricks at a
time without loosing your volume for IO.
These bricks may fail because of node crash or node disconnection. That is why
it is always good to have all the 6 bricks on 6 different nodes. If you have 3
bricks on one node and this nodes goes down then you
will loose the volume and it will be inaccessible. 
So just keep in mind that you should not loose more than redundancy bricks even
if any one node goes down.

---- 
Ashish 


----- Original Message -----

From: "Terry McGuire" <tmcguire at ualberta.ca> 
To: gluster-users at gluster.org 
Sent: Wednesday, March 29, 2017 11:59:32 PM 
Subject: [Gluster-users] Node count constraints with EC? 

Hello list. Newbie question: I?m building a low-performance/low-cost storage
service with a starting size of about 500TB, and want to use Gluster with
erasure coding. I?m considering subvolumes of maybe 4+2, or 8+3 or 4. I was
thinking I?d spread these over 4 nodes, and add single nodes over time, with
subvolumes rearranged over new nodes to maintain protection from whole node
failures.

However, reading through some RedHat-provided documentation, they seem to
suggest that node counts should be a multiple of 3, 6 or 12, depending on
subvolume config. Is this actually a requirement, or is it only a suggestion for
best performance or something?

Can anyone comment on node count constraints with erasure coded subvolumes? 

Thanks in advance for anyone?s reply, 
Terry 

_____________________________ 
Terry McGuire 
Information Services and Technology (IST) 
University of Alberta 
Edmonton, Alberta, Canada T6G 2H1 
Phone: 780-492-9422 


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Gluster-users mailing list 
Gluster-users at gluster.org 
http://lists.gluster.org/mailman/listinfo/gluster-users 

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> Le 29 mars 2017 ? 20:29, Terry McGuire <tmcguire at ualberta.ca> a
?crit :
> 
> I was thinking I?d spread these over 4 nodes, and add single nodes over
time, with subvolumes rearranged over new nodes to maintain protection from
whole node failures.
Also keep in mind that dispersed cluster can only be expanded by the number of
initial nodes, eg starting with 4 nodes 3+1 can only evolve by adding 4 nodes
3+1, you cannot change the default policy 3+1 to 4+1. So the granularity of the
evolution of the cluster is fixed at the beginning.

Cheers