12.4. Attaching a Tier to a Volume

By default, tiering is not enabled on gluster volumes. An existing volume can be modified via a CLI command to have a hot-tier. You must enable a volume by performing an attach tier operation. The attach command will declare an existing volume as cold-tier and creates a new hot-tier volume which is appended to it. Together, the combination is a single cache tiered volume.
It is highly recommended to provision your storage liberally and generously before attaching a tier. You create a normal volume and then attach bricks to it, which are the hot tier:
  1. Attach the tier to the volume by executing the following command:
    # gluster volume tier VOLNAME attach [replica COUNT] NEW-BRICK...
    For example,
    # gluster volume tier test-volume attach replica 2 server1:/exp1/tier1 server1:/exp2/tier2
    server2:/exp3/tier3 server2:/exp4/tier4
  2. Run gluster volume info command to optionally display the volume information.
    The command output displays information similar to the following:
    # gluster volume info test-volume
    Volume Name: test-volume
    Type: Tier
    Status: Started
    Number of Bricks: 8
    Transport-type: tcp
    Hot Tier :
    Hot Tier Type : Distributed-Replicate
    Number of Bricks: 2 x 2 = 4
    Brick1: server1:/exp1/tier1 
    Brick2: server1:/exp2/tier2
    Brick3: server2:/exp3/tier3
    Brick4: server2:/exp4/tier4
    Cold Tier:
    Cold Tier Type : Distributed-Replicate
    Number of Bricks: 2 x 2 = 4
    Brick5: server1:/exp1/brick1
    Brick6: server1:/exp2/brick2
    Brick7: server2:/exp3/brick3
    Brick8: server2:/exp4/brick4 
    Options Reconfigured:
    cluster.watermark-low: 70
    cluster.watermark-hi: 90
    cluster.tier-demote-frequency: 45
    cluster.tier-mode: cache
    features.ctr-enabled: on
    performance.readdir-ahead: on
The tier start command is triggered automatically after the tier has been attached. In some cases, if the tier process has not started you must start it manually using the gluster volume tier VOLNAME start force command.

12.4.1. Attaching a Tier to a Geo-replicated Volume

You can attach a tier volume to the master volume of the geo-replication session for better performance.

Important

A crash has been observed in the Slave mounts when performance.quick-read option is enabled and geo-replicated from a tiered master volume. If the master volume is a tiered volume, you must disable the performance.quick-read option in the Slave Volume using the following command:
# gluster volume set Slavevol performance.quick-read off
  1. Stop geo-replication between the master and slave, using the following command:
    # gluster volume geo-replication MASTER_VOL SLAVE_HOST::SLAVE_VOL stop
    For example:
    # gluster volume geo-replication Volume1 example.com::slave-vol stop
  2. Attach the tier to the volume using the following command:
    # gluster volume tier VOLNAME attach [replica COUNT] NEW-BRICK...
    For example, to create a distributed-replicated tier volume with replica count two:
    # gluster volume tier test-volume attach replica 2 server1:/exp1/tier1 server1:/exp2/tier2
    server2:/exp3/tier3 server2:/exp4/tier4
  3. Restart the geo-replication sessions, using the following command:
    # gluster volume geo-replication MASTER_VOL SLAVE_HOST::SLAVE_VOL start
    For example
    # gluster volume geo-replication Volume1 example.com::slave-vol start
  4. Verify whether geo-replication session has started with tier's bricks, using the following command:
    # gluster volume geo-replication MASTER_VOL SLAVE_HOST::SLAVE_VOL status
    For example,
    # gluster volume geo-replication Volume1 example.com::slave-vol status