[Gluster-users] number of bricks given doesn't match required count

Florent Bautista florent at coppint.com
Fri Feb 14 16:56:17 UTC 2014

On 02/14/2014 05:11 PM, Kaleb S. KEITHLEY wrote:
> With 4 bricks (brick = node + volume) and "replica 3" you'd only have
> a replica of one of your bricks, the other two would not be protected.

I really don't understand what you call "replica" so...
"replica" is replica of what ? Of brick ? of files ?
In my mind, "replica 3" means "each file is replicated 3 times in 3
different bricks". This is not that ?
So I don't understand what you mean by "you'd only have a replica of one
of your bricks, the other two would not be protected.".
If it's replicas of bricks, it means I have 2 "usable" bricks, the other
two are replicas of the first brick.

> But let's imagine that your first three bricks are 1TB disks, and the
> fourth is a 3TB disk. You could split the 3TB disk, e.g. with LVM,
> into three volumes to use as bricks to give you the full ×3
> replication required by gluster replication.

Ok but what the interest of having multiple bricks on a single node ? If
the node fails, you have 3 bricks out of service... I don't see what's
interesting here. The problem is that GlusterFS works on "bricks" and
not on nodes. Replicas can be on different bricks but on the same node,
for me it's absolutely a nonsense.

> Also Gluster's stripe is not the same as RAID-0. While similar, it
> doesn't give the performance improvement that real RAID-0 striping
> gives. I'd use gluster's stripe only if I have files that are so large
> they won't fit on a single brick. If you just want greater capacity
> for regular files you should use distribute (dht).

Ok, I understand this part :) I want to use stripping to have more data
security (whatever the performance), meaning if one node is hacked, the
attacker cannot see the whole content of files, just some stripes.

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