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Get started with GlusterFS - considerations and installation

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This article is updated to cover GlusterFS® 7 installation on CentOS® 7 and Ubuntu® 18.04. All the original work in this document is the same, except for the step where you create the volume with the replica keyword.

Before you start to use GlusterFS, you must decide what type of volume you need for your environment. The following methods are used most often to achieve different results.

Replicated volume

This type of volume provides file replication across multiple bricks. It is the best choice for environments requiring high availability, high reliability, and scalable storage. This volume type works well if you plan to self-mount the GlusterFS volume, for example, as the web server document root (/var/www) or similar where all files must reside on that node. The value passed to replica is the same number of nodes in the volume.

Files are copied to each brick in the volume, similar to a redundant array of independent disks (RAID-1). However, you can have three or more bricks or an odd number of bricks. Usable space is the size of one brick, and all files written to one brick are replicated to all others. Volumes of this type also offer improved read performance in most environments and are the most common type of volumes used when clients are external to the GlusterFS nodes themselves.

Distributed-replicated volume

Similar to a RAID-10, an even number of bricks must be used. Usable space is the size of the combined bricks passed to the replica value. For example, if there are four bricks of 20 Gigabytes (GB) and you pass replica 2 to the creation, your files are distributed to two nodes (40 GB) and replicated to two nodes. With six bricks of 20 GB and replica 3, your files are distributed to three nodes (60 GB) and replicated to three nodes. If you used replica 2, they are then distributed to two nodes (40 GB) and replicated to four nodes in pairs. This distribution and replication are used when your clients are external to the cluster, not local self-mounts.

Prerequisites

  • Two or more servers with separate storage. The examples in this article are based on CentOS 7 and Ubuntu 18.04 servers.
  • A private network between servers. The examples in this article use 192.168.0.0/24.

Build setup

The build described in this document uses the following setup:

  • Four Rackspace Cloud server images with a /dev/xvde partition ready to use for each brick
  • One Cloud Private Network on 192.168.0.0/24 for GlusterFS communication
  • GlusterFS 7.1 installed from the vendor package repository

Preparing the servers

Perform the following configuration and installations to prepare the servers:

  1. Configure /etc/hosts.
  2. Install the operating system (OS) updates.
  3. Install GlusterFS software.
  4. Configure network access.
  5. Connect GlusterFS nodes.

Configure /etc/hosts for intra-node communication

Instead of using DNS, prepare /etc/hosts on every server and ensure that the servers can communicate with each other. All servers have the name glusterN as a host name, so use glusN for the private communication layer between servers.

# vi /etc/hosts
192.168.0.1  glus-01
192.168.0.2  glus-02
192.168.0.3  glus-03
192.168.0.4  glus-04

# ping -c2 glus-01; ping -c2 glus-02;  ping -c2 glus-03;  ping -c2 glus-04

Install packages

Run the commands in this section to perform the following steps:

  1. Install OS updates.
  2. Install the GlusterFS repository and GlusterFS packages.

CentOS

yum update -y
yum install -y centos-release-gluster7
yum install -y glusterfs-server

Ubuntu operating system

The default Ubuntu repository has GlusterFS 3.13.2 installed. Use the following commands to install 7.1:

apt update
apt upgrade -y
add-apt-repository -y ppa:gluster/glusterfs-7
apt install -y glusterfs-server

Configure network access

CentOS

Use the following commands to allow Gluster traffic between your nodes and allow client mounts:

firewall-cmd --add-service=glusterfs
firewall-cmd --add-service=glusterfs --permanent

Ubuntu operating system

Use the following commands to allow all traffic over your private network segment to facilitate Gluster communication:

ufw enable
ufw allow from 192.168.0.0/24

Prepare the bricks

Run the commands in this section to perform the following steps:

  1. Partition block devices.
  2. Create the logical volume manager (LVM) foundation.
  3. Prepare volume bricks.

The underlying bricks are a standard file system and mount point. Mount each brick in such a way to discourage any user from changing to the directory and writing to the underlying bricks themselves.

Warning: Writing directly to a brick corrupts the volume.

The bricks must be unique per node, and there should be a directory within the mount point to use in volume creation. Attempting to create a replicated volume by using the top level of the mount points results in an error with instructions to use a subdirectory.

All nodes

parted -s -- /dev/xvde mktable gpt
parted -s -- /dev/xvde mkpart primary 2048s 100%
parted -s -- /dev/xvde set 1 lvm on
pvcreate /dev/xvde1
vgcreate vgglus-01 /dev/xvde1
lvcreate -l 100%VG -n gbrick1 vgglus-01
mkfs.xfs /dev/vgglus-01/gbrick1
echo '/dev/vgglus-01/gbrick1 /var/lib/gvol0 xfs defaults 0 0' >> /etc/fstab
mkdir /var/lib/gvol0
mount /var/lib/gvol0

  • glus-01

     mkdir /var/lib/gvol0/brick1

  • glus-02

     mkdir /var/lib/gvol0/brick2

  • glus-03

     mkdir /var/lib/gvol0/brick3

  • glus-04

     mkdir /var/lib/gvol0/brick4

Set up GlusterFS

Use the steps below to run the GlusterFS setup.

Start the glusterfsd daemon

You can restart the daemon at run time by using the following commands:

systemctl enable glusterd
systemctl start glusterd

Build a peer group

A peer group is known as a trusted storage pool in GlusterFS.

  • glus-01

    gluster peer probe glus-02
gluster peer probe glus-03
gluster peer probe glus-04
gluster peer status

  • glus-02

    gluster peer status

  • glus-03

    gluster peer status

  • glus-04

    gluster peer status

Now you can verify the status of your node and the gluster server pool:

[root@gluster1 ~]# gluster pool list
UUID	                				Hostname	State
734aea4c-fc4f-4971-ba3d-37bd5d9c35b8	glus-04   	Connected
d5c9e064-c06f-44d9-bf60-bae5fc881e16	glus-03   	Connected
57027f23-bdf2-4a95-8eb6-ff9f936dc31e	glus-02   	Connected
e64c5148-8942-4065-9654-169e20ed6f20	localhost	Connected

Create the volume

By default, glusterd NFS allows global read/write during volume creation, so you should set up basic authorization restrictions to only the private subnet. glusterd automatically starts NFSd on each server and exports the volume through it from each of the nodes. The reason for this behavior is that to use the native client Filesystem in Userspace (FUSE) for mounting the volume on clients, the clients have to run exactly the same version of GlusterFS packages. If the versions are different, there could be differences in the hashing algorithms used by servers and clients, and the clients won't be able to connect.

Replicated volume

The following example creates replication to all four nodes. Each node contains a copy of all data, and the size of the volume is the size of a single brick. Note that the output shows 1 x 4 = 4.

One node only:

 gluster volume create gvol0 replica 4 transport tcp \
 glus-01:/var/lib/gvol0/brick1 \
 glus-02:/var/lib/gvol0/brick2 \
 glus-03:/var/lib/gvol0/brick3 \
 glus-04:/var/lib/gvol0/brick4
 gluster volume start gvol0

[root@gluster1 ~]# gluster volume info gvol0

Volume Name: gvol0
Type: Replicate
Volume ID: 8d12cb5a-77ad-43a3-bdd1-ab48405ff1da
Status: Started
Snapshot Count: 0
Number of Bricks: 1 x 4 = 4
Transport-type: tcp
Bricks:
Brick1: glus-01:/var/lib/gvol0/brick1
Brick2: glus-02:/var/lib/gvol0/brick2
Brick3: glus-03:/var/lib/gvol0/brick3
Brick4: glus-04:/var/lib/gvol0/brick4
Options Reconfigured:
transport.address-family: inet
storage.fips-mode-rchecksum: on
performance.client-io-threads: off

Distributed-replicated volume

This example creates distributed replication to 2x2 nodes. Each pair of nodes contains the data, and the size of the volume is the size of two bricks. Note that the output shows 2 x 2 = 4.

One node only:

gluster volume create gvol0 replica 2 transport tcp \
glus-01:/var/lib/gvol0/brick1 \
glus-02:/var/lib/gvol0/brick2 \
glus-03:/var/lib/gvol0/brick3 \
glus-04:/var/lib/gvol0/brick4
gluster volume start gvol0

[root@gluster1 ~]# gluster volume info gvol0

Volume Name: gvol0
Type: Distributed-Replicate
Volume ID: b2ddd34b-ffb4-4fd8-ae60-b90adbd4c2ab
Status: Started
Snapshot Count: 0
Number of Bricks: 2 x 2 = 4
Transport-type: tcp
Bricks:
Brick1: glus-01:/var/lib/gvol0/brick1
Brick2: glus-02:/var/lib/gvol0/brick2
Brick3: glus-03:/var/lib/gvol0/brick3
Brick4: glus-04:/var/lib/gvol0/brick4
Options Reconfigured:
transport.address-family: inet
storage.fips-mode-rchecksum: on
performance.client-io-threads: off

Delete the volume

After you ensure that no clients (either local or remote) are mounting the volume, you can stop the volume and delete it by using the following commands:

gluster volume stop gvol0
gluster volume delete gvol0

Clearing bricks

If bricks are used in a volume and they need to be removed, you can use one of the following methods:

GlusterFS sets an attribute on the brick subdirectories. If you clear this attribute the bricks can be reused.

  • glus-01:

    setfattr -x trusted.glusterfs.volume-id /var/lib/gvol0/brick1/
    setfattr -x trusted.gfid /var/lib/gvol0/brick1
    rm -rf /var/lib/gvol0/brick1/.glusterfs

  • glus-02:

    setfattr -x trusted.glusterfs.volume-id /var/lib/gvol0/brick2/
    setfattr -x trusted.gfid /var/lib/gvol0/brick2
    rm -rf /var/lib/gvol0/brick2/.glusterfs

  • glus-03:

    setfattr -x trusted.glusterfs.volume-id /var/lib/gvol0/brick3/
    setfattr -x trusted.gfid /var/lib/gvol0/brick3
    rm -rf /var/lib/gvol0/brick3/.glusterfs

  • glus-04:

    setfattr -x trusted.glusterfs.volume-id /var/lib/gvol0/brick4/
    setfattr -x trusted.gfid /var/lib/gvol0/brick4
    rm -rf /var/lib/gvol0/brick4/.glusterfs

Alternatively, you can delete the subdirectories and then recreate them.

  • glus-01

    rm -rf /var/lib/gvol0/brick1
    mkdir /var/lib/gvol0/brick1

  • glus-02:

    rm -rf /var/lib/gvol0/brick2
    mkdir /var/lib/gvol0/brick2

  • glus-03:

    rm -rf /var/lib/gvol0/brick3
    mkdir /var/lib/gvol0/brick3

  • glus-04:

    rm -rf /var/lib/gvol0/brick4
    mkdir /var/lib/gvol0/brick4

Add bricks

You can add more bricks to a running volume. Add an additional brick to our replicated volume example above by using the following command:

gluster volume add-brick gvol0 replica 5 gluster5:/var/lib/gvol0/brick5

YOu can use the add-brick command to change the layout of your volume, for example, to change a two-node distributed volume into a four-node distributed-replicated volume. After such an operation, you must rebalance your volume. New files are automatically created on the new nodes, but the old ones do not get moved.

gluster volume add-brick gvol0 replica 2 \
gluster5:/var/lib/gvol0/brick5 ;
gluster6:/var/lib/gvol0/brick6
gluster volume rebalance gvol0 start
gluster volume rebalance gvol0 status

## If needed (something didn't work right)
gluster volume rebalance gvol0 stop

Volume options

To view configured volume options, run the following command:

gluster volume info gvol0

The following is an example output:

Volume Name: gvol0
Type: Replicate
Volume ID: 8d12cb5a-77ad-43a3-bdd1-ab48405ff1da
Status: Started
Snapshot Count: 0
Number of Bricks: 1 x 4 = 4
Transport-type: tcp
Bricks:
Brick1: glus-01:/var/lib/gvol0/brick1
Brick2: glus-02:/var/lib/gvol0/brick2
Brick3: glus-03:/var/lib/gvol0/brick3
Brick4: glus-04:/var/lib/gvol0/brick4
Options Reconfigured:
transport.address-family: inet
storage.fips-mode-rchecksum: on
performance.client-io-threads: off

To set an option for a volume, use the set keyword as follows:

gluster volume set gvol0 performance.write-behind off
volume set: success

To clear an option to a volume back to the default, use the reset keyword as follows:

gluster volume reset gvol0 performance.read-ahead
volume reset: success: reset volume successful

Client mounts

The preferred method for a client to mount a GlusterFS volume is by using the native FUSE client. NFS mounts are possible when GlusterFS is deployed in tandem with NFS-Ganesha®.

FUSE client

The FUSE client allows the mount to happen with a GlusterFS "round robin" style connection. In /etc/fstab, the name of one node is used. However, internal mechanisms allow that node to fail, and the clients roll over to other connected nodes in the trusted storage pool.

CentOS:

yum install -y centos-release-gluster7
yum install -y glusterfs-fuse

Ubuntu:

add-apt-repository -y ppa:gluster/glusterfs-7
apt install glusterfs-client

Common:

vi /etc/hosts
192.168.0.2  glus-01
192.168.0.4  glus-02
192.168.0.1  glus-03
192.168.0.3  glus-04

`modprobe fuse
 echo 'glus-01:/gvol0 /mnt/gluster/gvol0 glusterfs _netdev 0 0' >> /etc/fstab
 mkdir -p /mnt/gluster/gvol0
 mount /mnt/gluster/gvol0`

References

Next article

GlusterFS Troubleshooting

Updated about 1 year ago