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

[Gandalf Corvotempesta]

Il 09 ago 2016 19:57, "Ashish Pandey" <aspandey at redhat.com> ha scritto:
> Yes, redundant data spread across multiple servers. In my example I
mentioned 6 different nodes each with one brick.
> Point is that for 4+2 you can loose any 2 bricks. It could be because of
node failure or brick failure.
> 1 - 6 bricks on 6 different nodes - any 2 nodes may go down - EC win
>
> However if you have only 2 nodes and 3 bricks on each nodes, then yes in
this case even if one node goes down, ec will fail because that will cause
3 bricks down.
> In this case replica 3 would win.

6 nodes with 1 brick each is a surreal case.
A much common case is multiple nodes with multiple bricks, something like 9
nodes with 12 bricks each. (In example,  a 2U supermicro server with 12
disks)

In this case, EC replicas could be placed on a single server.

And with 9*12 bricks you still have 2 single disks (or one server if both
are placed on the same hardware) as failure domains.
Yes, you'll get 9*(12-2) usable bricks and not (9*12)/3 but you risk data
loss for sure.

Just a question:  with EC which is the right calc method between these 3:

a)  (#servers*#bricks)-#replicas

Or

b) #servers*(#bricks - #replicas)

Or

c) (#servers-#replicas)*#bricks

In case A I'll use 2 disks as replica for the whole volume (exactly like a
raid6)

In case B I'll use 2 disks from each server as replica

in case C I'll use 2 whole servers as replica (this is the most secure as i
can loose 2 whole servers)
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