On 21/09/16 14:36, Gandalf Corvotempesta wrote:
Il 01 set 2016 10:18 AM, "Xavier Hernandez" <xhernan...@datalab.es
<mailto:xhernan...@datalab.es>> ha scritto:
If you put more than one fragment into the same server, you will lose
all the fragments if the server goes down. If there are more than 4
fragments on that server, the file will be unrecoverable until the
server is brought up again.

Putting more than one fragment into a single server only makes sense
to account for disk failures, since the protection against server
failures is lower.

Exactly, what i would like to ensure is that the 4 segments needed for
recovery are placed automatically on at least 4 servers (and not on 4
different bricks that could be on the same server)

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.

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