Re: [Gluster-devel] Is it possible to setup a RAID 6 using GlusterFS?

[Pascal]

Hello David,

thank you for explaining it. 

To sum it up: Your suggestion works like a charm ;)

I still have a follow-up question. I expected the available storage
capacity to be half of the total storage capacity provided by all brick
partitions/volumes.

In my test environment each of the four bricks provides ~16 GB and if
two nodes could fail at the same time, there would just ~32 GB be left. 

So I used the df command on a client ...
# df -h /mn/gluster-volume
... and it shows me that ~64 GB are available.

I am not able to store files of a total size of 64 GB on that volume,
isn't it? Can someone explain the result of df to me?


----------


I am not sure, if it is the usual way to write down "solutions" on the
mailing list, but I thing it could be helpful for other people. 

node1
- /data
  - /exp1
  - /exp2
  - /exp3

node2
- /data
  - /exp1
  - /exp2
  - /exp3

node3
- /data
  - /exp1
  - /exp2
  - /exp3

node4
- /data
  - /exp1
  - /exp2
  - /exp3

# gluster volume create gluster-volume replica 3 transport tcp \
node1:/data/exp1 node2:/data/exp1 node3:/data/exp1 \
node1:/data/exp2 node2:/data/exp2 node4:/data/exp1 \
node1:/data/exp3 node3:/data/exp2 node4:/data/exp2 \
node2:/data/exp3 node3:/data/exp3 node4:/data/exp3


Am Fri, 06 Apr 2012 21:04:16 -0400
schrieb David Coulson <address@hidden>:

> You need to do 12 bricks across 4 nodes, in 'replica 3' groups. This 
> would allow you to lose two nodes and still have access to all your 
> data, as each distributed replica group is across at least 3 of your
> 4 nodes.
> 
> You will need to be deliberate about which 3-way groups end up on
> each node so you have appropriate redundancy (e.g. group one does
> 1,2,3, group two does 1,3,4, three does 2,3,4, four does 1,2,4)
> 
> On 4/6/12 8:06 PM, Pascal wrote:
> > Hello David,
> >
> > I hope that you will read this, even though your post was written
> > some days ago.
> >
> > I was trying to configure your suggestion "with a replica count of
> > 3" and I wasn't able to do it.
> >
> >
> > My original setup with four nodes: node1, node2, node3, node4.
> >
> > # gluster volume create gluster-storage replica 2 transport tcp
> > ip-node1:/data ip-node2:/data ip-node3:/data ip-node4:/data
> >
> > The result:
> > Node1 and node2 replicated the files among each other and node3 and
> > node4 did the same. The replication group of node1 and node2
> > (group1) distributed the files among the replication group of node3
> > and node4 (group2).
> >
> > The problem:
> > Two hard drives could fail at the same time, but just one hard drive
> > from each replication group. My aim is to archive something were
> > any two hard drives could fail.
> >
> >
> > Trying to setup a replica count of 3 with my four nodes:
> >
> > # gluster volume create gluster-storage replica 3 transport tcp
> > ip-node1:/data ip-node2:/data ip-node3:/data ip-node4:/data
> >> number of bricks is not a multiple of replica count
> > This means to my, that I would need six nodes/bricks and that would
> > lead me to the same situation as before. Node1, node2 and node3
> > would build a replication group and node4, node5 and node6 would
> > build the other replication group and both groups together would
> > save all the data.
> > I would still have the problem that two hard drives from one
> > replication group weren't allowed to fail at the same time.
> >
> >
> > Did I misunderstood your idea of a "replica count of 3"? Would you
> > be so kind to explain it to me?
> >
> > Thanks in advance!
> >
> > Pascal
> >
> >
> > Am Thu, 29 Mar 2012 10:47:38 -0400
> > schrieb David
> > Coulson<address@hidden>:
> >
> >> Try doing a distributed-replica with a replica count of 3. Not
> >> really 'RAID-6' comparable, but you can have two nodes fail
> >> without outage.
> >>
> >> http://download.gluster.com/pub/gluster/glusterfs/3.2/Documentation/AG/html/sect-Administration_Guide--Setting_Volumes-Distributed_Replicated.html
> >>
> >> On 3/29/12 10:39 AM, Pascal wrote:
> >>> Hello everyone,
> >>>
> >>> I would like to know if it is possible to setup a GlusterFS
> >>> installation which is comparable to a RAID 6? I did some research
> >>> in the community and several mailing lists and all I could find
> >>> were the similar request from 2009
> >>> (http://gluster.org/pipermail/gluster-users/2009-May/002208.html,
> >>> http://www.gluster.org/community/documentation/index.ph/Talk:GlusterFS_Roadmap_Suggestions).
> >>>
> >>> I would just like to have a scenario where two GlusterFS
> >>> nodes/servers, respectively their hard drives, could fail at the
> >>> same time.
> >>>
> >>> Thanks in advance!
> >>> Pascal