[Gluster-users] how many hosts could be down in a 12x(4+2) distributed dispersed volume?

[Mauro Tridici]

Dear Ashish,

thank you very much for the information and for the provided examples. They really help.

I think that it may be useful to stick a label on each server in order to identify the group they belong to.
For example:

server n.01 (label: Group 01)
server n.02 (label: Group 01)
server n.03 (label: Group 01)

server n.04 (label: Group 02)
server n.05 (label: Group 02)
server n.06 (label: Group 02)

So, if server n.01 and server n.06 go down I know that there will be no problem for the data.
But, if server n.05 and n.06 go down, I can start to cry.

Thank you again,
Mauro Tridici

> Il giorno 20 set 2017, alle ore 09:33, Ashish Pandey <aspandey at redhat.com> ha scritto:
> 
> 
> After adding 3 more nodes you will have 6 nodes and 2 HD on each nodes.
> It depends on the way you are going to add new bricks on the existing volume 'vol"
> I think you should remember that in a given EC sub volume of 4+2, at any point of time 2 bricks could be down.
> When you make 6 * (4+2) to 12 * (4+2) you have to provide path of the bricks you want to add.
> 
> Suppose you want to add 6 bricks and all the 6 bricks are on 3 new nodes (2 each) then with respect to that sub volume  you can tolerate 1 node going down. 
> If you are creating a 12 * (4+2) volume from the scratch and providing 12 bricks from each server then in that case even 2 nodes can go down without any issue.
> 
> I think You should focus more on the number of Hard Drive in a sub volume. You should ask yourself "How many bricks (HD) with in a  sub volume will be unavailable if 1 or 2 nodes are going down?"
> 
> Ashish
> 
> 
> 
> 
> From: "Mauro Tridici" <mauro.tridici at cmcc.it>
> To: gluster-users at gluster.org
> Sent: Tuesday, September 19, 2017 1:09:06 AM
> Subject: [Gluster-users] how many hosts could be down in a 12x(4+2)        distributed dispersed volume?
> 
> Dear All,
> 
> I just implemented a (6x(4+2)) DISTRIBUTED DISPERSED gluster (v.3.10) volume based on the following hardware:
> 
> - 3 gluster servers (each server with 2 CPU 10 cores, 64GB RAM, 12 hard disk SAS 12Gb/s, 10GbE storage network)
> 
> Now, we need to add 3 new servers with the same hardware configuration respecting the current volume topology.
> 
> 
> My question is: in the current volume configuration, only 2 bricks per subvolume or one host could be down without losing data. What it will happen in the next configuration? How many hosts could be down without losing data?
> 
> Thank you very much.
> Mauro Tridici
> 
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-------------------------
Mauro Tridici

Fondazione CMCC
CMCC Supercomputing Center
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email: mauro.tridici at cmcc.it

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