[Gluster-users] EC clarification

[Gandalf Corvotempesta]

2016-09-21 14:42 GMT+02:00 Xavier Hernandez <xhernandez at datalab.es>:
> You *must* ensure that *all* bricks forming a single disperse set are placed
> in a different server. There are no 4 special fragments. All fragments have
> the same importance. The way to do that is ordering them when the volume is
> created:
>
> gluster volume create test disperse 16 redundancy 4
> server{1..20}:/bricks/test1 server{1..20}:/bricks/test2
> server{1..20}:/bricks/test3
>
> This way all 20 fragments from each disperse set will be placed in a
> different server. However each server will have 3 bricks and no fragment
> from a single file will be stored in more than one brick of each server.

Now it's clear.
So, at very minimum, EC is good starting from 7+3 (10 servers with 1
brick each) because: 512*(7-3) = 2048
Any smaller combinations would mean less redundancy (6+2) or not
optimized stripe size like 512*(5-3)=1024

Is this correct ? And what if I have to add some brick to the current
servers or I have to add new servers?
Can I add them freely or I have to follow some rules ?