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Configure Firewall

For the Gluster to communicate within a cluster either the firewalls have to be turned off or enable communication for each server.

iptables -I INPUT -p all -s `<ip-address>` -j ACCEPT

Configure the trusted pool

Remember that the trusted pool is the term used to define a cluster of nodes in Gluster. Choose a server to be your “primary” server. This is just to keep things simple, you will generally want to run all commands from this tutorial. Keep in mind, running many Gluster specific commands (like gluster volume create) on one server in the cluster will execute the same command on all other servers.

Replace nodename with hostname of the other server in the cluster, or IP address if you don’t have DNS or /etc/hosts entries. Let say we want to connect to node02:

gluster peer probe node02

Notice that running gluster peer status from the second node shows that the first node has already been added.

Partition the disk

Assuming you have an empty disk at /dev/sdb: (You can check the partitions on your system using fdisk -l)

fdisk /dev/sdb

And then create a single XFS partition using fdisk

Format the partition

mkfs.xfs -i size=512 /dev/sdb1

Add an entry to /etc/fstab

echo "/dev/sdb1 /export/sdb1 xfs defaults 0 0"  >> /etc/fstab

Mount the partition as a Gluster "brick"

mkdir -p /export/sdb1 && mount -a

Set up a Gluster volume

The most basic Gluster volume type is a “Distribute only” volume (also referred to as a “pure DHT” volume if you want to impress the folks at the water cooler). This type of volume simply distributes the data evenly across the available bricks in a volume. So, if I write 100 files, on average, fifty will end up on one server, and fifty will end up on another. This is faster than a “replicated” volume, but isn’t as popular since it doesn’t give you two of the most sought after features of Gluster — multiple copies of the data, and automatic failover if something goes wrong.

To set up a replicated volume:

gluster volume create gv0 replica 3 \                                   \

Breaking this down into pieces:

  • the first part says to create a gluster volume named gv0 (the name is arbitrary, gv0 was chosen simply because it’s less typing than gluster_volume_0).
  • make the volume a replica volume
  • keep a copy of the data on at least 3 bricks at any given time. Since we only have three bricks total, this means each server will house a copy of the data.
  • we specify which nodes to use, and which bricks on those nodes. The order here is important when you have more bricks.
  • the brick directory will be created by this command. If the directory already exists, you may get <brick> is already part of a volume errors.

It is possible (as of the most current release as of this writing, Gluster 3.3) to specify the bricks in such a way that you would make both copies of the data reside on a single node. This would make for an embarrassing explanation to your boss when your bulletproof, completely redundant, always on super cluster comes to a grinding halt when a single point of failure occurs.

Now, we can check to make sure things are working as expected:

gluster volume info

And you should see results similar to the following:

Volume Name: gv0
Type: Replicate
Volume ID: 8bc3e96b-a1b6-457d-8f7a-a91d1d4dc019
Status: Created
Number of Bricks: 1 x 3 = 3
Transport-type: tcp

This shows us essentially what we just specified during the volume creation. The one key output worth noticing is Status. A status of Created means that the volume has been created, but hasn’t yet been started, which would cause any attempt to mount the volume fail.

Now, we should start the volume before we try to mount it.

gluster volume start gv0