18.2. Provisioning Storage for Three-way Replication Volumes

Red Hat Storage supports synchronous three-way replication across three availability zones. Three-way replication is supported only with JBOD configuration. You must use one EBS volume as one storage brick. For information on best practices while configuring a JBOD, see Section 9.1.2, “JBOD”.
  1. Login to Amazon Web Services at http://aws.amazon.com and select the Amazon EC2 tab.
  2. Create six AWS instances in three different availability zones. All the bricks of a replica pair must be from different availability zones. For each replica set, select the instances for the bricks from three different availability zones. A replica pair must not have a brick along with its replica from the same availability zone.
  3. Add single EBS volume to each AWS instances
  4. Create a Logical Volume (LV) on each EBS volume using the following commands:
    # pvcreate /dev/xvdf1
    # vgcreate glustervg /dev/xvdf1
    # vgchange -a y glustervg
    # lvcreate -a y -l 100%VG -n glusterlv glustervg
    In these commands, /dev/xvdf1 is a EBS volume, glustervg is the name of the volume group and glusterlv is the name of the logical volume. Red Hat Storage uses the logical volume created over EBS as a brick. For more information about logical volumes, see the Red Hat Enterprise Linux Logical Volume Manager Administration Guide.
  5. Format the logical volume using the following command:
    # mkfs.xfs -i size=512 DEVICE
    For example, to format /dev/glustervg/glusterlv:
    # mkfs.xfs -i size=512 /dev/glustervg/glusterlv
  6. Mount the device using the following commands:
    # mkdir -p /export/glusterlv
    # mount /dev/glustervg/glusterlv /export/glusterlv
  7. Using the following command, add the device to /etc/fstab so that it mounts automatically when the system reboots:
    # echo "/dev/glustervg/glusterlv /export/glusterlv xfs defaults 0 2" >> /etc/fstab
Client-side Quorum
You must ensure to create each replica set of a volume in three difference zones. With this configuration, there will be no impact on the data availability even if two availability zones have hit an outage. However, when you set client-side quorum to avoid split-brain scenarios, unavailability of two zones would make the access read-only.
For information on creating three-way replicated volumes, see Section 6.5, “Creating Distributed Replicated Volumes”. For more information on configuring client-side quorum, see Section 8.10.1.2, “Configuring Client-Side Quorum”.