[Gluster-users] Need help to design a data storage

[Gandalf Corvotempesta]

Il 09 ago 2016 10:06 AM, "Ashish Pandey" <aspandey at redhat.com> ha scritto:
> If your main concern is data redundancy, I would suggest you to go for
erasure coded volume provided by gluster.

Anyway EC volumes has a lower redundancy level than standard replicated
volumes.

Let's assume a 9 nodes cluster with 12 disks on each node, redundancy set
to 2

You have 9*12 = 108 disks/bricks
with redundancy 2 you can loose up to 2 bricks/disks at the same time
before loosing data. Using cheap sata disks (gluster is made to run on
commodity hardware) loosing 3 disks over 108 in a very short time could
happen frequently and this frequency grow as cluster grows

With a standard replicated volume,  with replica 3, you can loose up to 3
servers (not bricks) because each brick in a replica set must be on a
different server.

I think EC is something like raid6 (with more "parity") and standard
replication is like raid10 but with 3 disks for each mirror.

Raid10 is safer as you can loose as many disks as you want,  if in
different replica set, while raid 6 can loose up to 2 disks in the whole
cluster
Higher the number of disks, higher the probability of data loss with
raid6/EC

Am i missed something?
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