Geo-replication provides a continuous, asynchronous, and incremental replication service from one site to another over Local Area Networks (LANs), Wide Area Network (WANs), and across the Internet. Geo-replication uses a master–slave model, whereby replication and mirroring occurs between the following partners: Master – a GlusterFS volume Slave – a slave which can be of the following types: A local directory which can be represented as file URL like file:///path/to/dir. You can use shortened form, for example, /path/to/dir. A GlusterFS Volume - Slave volume can be either a local volume like gluster://localhost:volname (shortened form - :volname) or a volume served by different host like gluster://host:volname (shortened form - host:volname). Both of the above types can be accessed remotely using SSH tunnel. To use SSH, add an SSH prefix to either a file URL or gluster type URL. For example, ssh://root@remote-host:/path/to/dir (shortened form - root@remote-host:/path/to/dir) or ssh://root@remote-host:gluster://localhost:volname (shortened from - root@remote-host::volname). This section introduces Geo-replication, illustrates the various deployment scenarios, and explains how to configure the system to provide replication and mirroring in your environment.

The following table lists the difference between replicated volumes and geo-replication: Replicated Volumes Geo-replication Mirrors data across clusters Mirrors data across geographically distributed clusters Provides high-availability Ensures backing up of data for disaster recovery Synchronous replication (each and every file operation is sent across all the bricks) Asynchronous replication (checks for the changes in files periodically and syncs them on detecting differences)

This section provides an overview of the Geo-replication deployment scenarios, describes how you can check the minimum system requirements, and explores common deployment scenarios.

Geo-replication provides an incremental replication service over Local Area Networks (LANs), Wide Area Network (WANs), and across the Internet. This section illustrates the most common deployment scenarios for Geo-replication, including the following: Geo-replication over LAN Geo-replication over WAN Geo-replication over the Internet Multi-site cascading Geo-replication Geo-replication over LAN You can configure Geo-replication to mirror data over a Local Area Network. Geo-replication over LAN Geo-replication over WAN You can configure Geo-replication to replicate data over a Wide Area Network. Geo-replication over WAN Geo-replication over Internet You can configure Geo-replication to mirror data over the Internet. Geo-replication over Internet Multi-site cascading Geo-replication You can configure Geo-replication to mirror data in a cascading fashion across multiple sites. Multi-site cascading Geo-replication

Deploying Geo-replication involves the following steps: Verify that your environment matches the minimum system requirement. For more information, see . Determine the appropriate deployment scenario. For more information, see . Start Geo-replication on master and slave systems, as required. For more information, see .

Before deploying GlusterFS Geo-replication, verify that your systems match the minimum requirements. The following table outlines the minimum requirements for both master and slave nodes within your environment: Component Master Slave Operating System GNU/Linux GNU/Linux Filesystem GlusterFS 3.2 or higher GlusterFS 3.2 or higher (GlusterFS needs to be installed, but does not need to be running), ext3, ext4, or XFS (any other POSIX compliant file system would work, but has not been tested extensively) Python Python 2.4 (with ctypes external module), or Python 2.5 (or higher) Python 2.4 (with ctypes external module), or Python 2.5 (or higher) Secure shell OpenSSH version 4.0 (or higher) SSH2-compliant daemon Remote synchronization rsync 3.0.7 or higher rsync 3.0.7 or higher FUSE GlusterFS supported versions GlusterFS supported versions

Time Synchronization On bricks of a geo-replication master volume, all the servers' time must be uniform. You are recommended to set up NTP (Network Time Protocol) service to keep the bricks sync in time and avoid out-of-time sync effect. For example: In a Replicated volume where brick1 of the master is at 12.20 hrs and brick 2 of the master is at 12.10 hrs with 10 minutes time lag, all the changes in brick2 between this period may go unnoticed during synchronization of files with Slave. For more information on setting up NTP, see . To setup Geo-replication for SSH Password-less login has to be set up between the host machine (where geo-replication Start command will be issued) and the remote machine (where slave process should be launched through SSH). On the node where geo-replication sessions are to be set up, run the following command: # ssh-keygen -f /etc/glusterd/geo-replication/secret.pem Press Enter twice to avoid passphrase. Run the following command on master for all the slave hosts: # ssh-copy-id -i /etc/glusterd/geo-replication/secret.pem.pub user@slavehost

You can configure a secure slave using SSH so that master is granted a restricted access. With GlusterFS, you need not specify configuration parameters regarding the slave on the master-side configuration. For example, the master does not require the location of the rsync program on slave but the slave must ensure that rsync is in the PATH of the user which the master connects using SSH. The only information that master and slave have to negotiate are the slave-side user account, slave's resources that master uses as slave resources, and the master's public key. Secure access to the slave can be established using the following options: Restricting Remote Command Execution Using Mountbroker for Slaves Using IP based Access Control Backward Compatibility Your existing Ge-replication environment will work with GlusterFS, except for the following: The process of secure reconfiguration affects only the glusterfs instance on slave. The changes are transparent to master with the exception that you may have to change the SSH target to an unprivileged account on slave. The following are the some exceptions where this might not work: Geo-replication URLs which specify the slave resource when configuring master will include the following special characters: space, *, ?, [; Slave must have a running instance of glusterd, even if there is no gluster volume among the mounted slave resources (that is, file tree slaves are used exclusively) .

If you restrict remote command execution, then the Slave audits commands coming from the master and the commands related to the given geo-replication session is allowed. The Slave also provides access only to the files within the slave resource which can be read or manipulated by the Master. To restrict remote command execution: Identify the location of the gsyncd helper utility on Slave. This utility is installed in PREFIX/libexec/glusterfs/gsyncd, where PREFIX is a compile-time parameter of glusterfs. For example, --prefix=PREFIX to the configure script with the following common values /usr, /usr/local, and /opt/glusterfs/glusterfs_version. Ensure that command invoked from master to slave passed through the slave's gsyncd utility. You can use either of the following two options: Set gsyncd with an absolute path as the shell for the account which the master connects through SSH. If you need to use a privileged account, then set it up by creating a new user with UID 0. Setup key authentication with command enforcement to gsyncd. You must prefix the copy of master's public key in the Slave account's authorized_keys file with the following command: command=<path to gsyncd>. For example, command="PREFIX/glusterfs/gsyncd" ssh-rsa AAAAB3Nza....

mountbroker is a new service of glusterd. This service allows an unprivileged process to own a GlusterFS mount by registering a label (and DSL (Domain-specific language) options ) with glusterd through a glusterd volfile. Using CLI, you can send a mount request to glusterd to receive an alias (symlink) of the mounted volume. A request from the agent , the unprivileged slave agents use the mountbroker service of glusterd to set up an auxiliary gluster mount for the agent in a special environment which ensures that the agent is only allowed to access with special parameters that provide administrative level access to the particular volume. To setup an auxiliary gluster mount for the agent: Create a new group. For example, geogroup. Create a unprivileged account. For example, geoaccount. Make it a member of geogroup. Create a new directory owned by root and with permissions 0711. For example, create a create mountbroker-root directory /var/mountbroker-root. Add the following options to the glusterd volfile, assuming the name of the slave gluster volume as slavevol: option mountbroker-root /var/mountbroker-root option mountbroker-geo-replication.geoaccount slavevol option geo-replication-log-group geogroup If you are unable to locate the glusterd volfile at /etc/glusterfs/glusterd.vol, you can create a volfile containing both the default configuration and the above options and place it at /etc/glusterfs/. A sample glusterd volfile along with default options: volume management type mgmt/glusterd option working-directory /etc/glusterd option transport-type socket,rdma option transport.socket.keepalive-time 10 option transport.socket.keepalive-interval 2 option transport.socket.read-fail-log off option mountbroker-root /var/mountbroker-root option mountbroker-geo-replication.geoaccount slavevol option geo-replication-log-group geogroup end-volume If you host multiple slave volumes on Slave, you can repeat step 2. for each of them and add the following options to the volfile: option mountbroker-geo-replication.geoaccount2 slavevol2 option mountbroker-geo-replication.geoaccount3 slavevol3 Setup Master to access Slave as geoaccount@Slave. You can add multiple slave volumes within the same account (geoaccount) by providing comma-separated list (without spaces) as the argument of mountbroker-geo-replication.geogroup. You can also have multiple options of the form mountbroker-geo-replication.*. It is recommended to use one service account per Master machine. For example, if there are multiple slave volumes on Slave for the master machines Master1, Master2, and Master3, then create a dedicated service user on Slave for them by repeating Step 2. for each (like geogroup1, geogroup2, and geogroup3), and then add the following corresponding options to the volfile: option mountbroker-geo-replication.geoaccount1 slavevol11,slavevol12,slavevol13 option mountbroker-geo-replication.geoaccount2 slavevol21,slavevol22 option mountbroker-geo-replication.geoaccount3 slavevol31 Now set up Master1 to ssh to geoaccount1@Slave, etc. You must restart glusterd after making changes in the configuration to effect the updates.

You can use IP based access control method to provide access control for the slave resources using IP address. You can use method for both Slave and file tree slaves, but in the section, we are focusing on file tree slaves using this method. To set access control based on IP address for file tree slaves: Set a general restriction for accessibility of file tree resources: # gluster volume geo-replication '/*' config allow-network ::1,127.0.0.1 This will refuse all requests for spawning slave agents except for requests initiated locally. If you want the to lease file tree at /data/slave-tree to Master, enter the following command: # gluster volume geo-replication /data/slave-tree config allow-network MasterIP MasterIP is the IP address of Master. The slave agent spawn request from master will be accepted if it is executed at /data/slave-tree. If the Master side network configuration does not enable the Slave to recognize the exact IP address of Master, you can use CIDR notation to specify a subnet instead of a single IP address as MasterIP or even comma-separated lists of CIDR subnets. If you want to extend IP based access control to gluster slaves, use the following command: # gluster volume geo-replication '*' config allow-network ::1,127.0.0.1

This section describes how to configure and start Gluster Geo-replication in your storage environment, and verify that it is functioning correctly.

To start Gluster Geo-replication Start geo-replication between the hosts using the following command: # gluster volume geo-replication MASTER SLAVE start For example: # gluster volume geo-replication Volume1 example.com:/data/remote_dir start Starting geo-replication session between Volume1 example.com:/data/remote_dir has been successful You may need to configure the service before starting Gluster Geo-replication. For more information, see .

You can use the gluster command to verify the status of Gluster Geo-replication in your environment. To verify the status Gluster Geo-replication Verify the status by issuing the following command on host: # gluster volume geo-replication MASTER SLAVE status For example: # gluster volume geo-replication Volume1 example.com:/data/remote_dir status # gluster volume geo-replication Volume1 example.com:/data/remote_dir status MASTER SLAVE STATUS ______ ______________________________ ____________ Volume1 root@example.com:/data/remote_dir Starting....

You can display status information about a specific geo-replication master session, or a particular master-slave session, or all geo-replication sessions, as needed. To display geo-replication status information Display information of all geo-replication sessions using the following command: # gluster volume geo-replication Volume1 example.com:/data/remote_dir status MASTER SLAVE STATUS ______ ______________________________ ____________ Volume1 root@example.com:/data/remote_dir Starting.... Display information of a particular master slave session using the following command: # gluster volume geo-replication MASTER SLAVE status For example, to display information of Volume1 and example.com:/data/remote_dir # gluster volume geo-replication Volume1 example.com:/data/remote_dir status The status of the geo-replication between Volume1 and example.com:/data/remote_dir is displayed. Display information of all geo-replication sessions belonging to a master # gluster volume geo-replication MASTER status For example, to display information of Volume1 # gluster volume geo-replication Volume1 example.com:/data/remote_dir status MASTER SLAVE STATUS ______ ______________________________ ____________ Volume1 ssh://example.com:gluster://127.0.0.1:remove_volume OK Volume1 ssh://example.com:file:///data/remote_dir OK The status of a session could be one of the following four: Starting: This is the initial phase of the Geo-replication session; it remains in this state for a minute, to make sure no abnormalities are present. OK: The geo-replication session is in a stable state. Faulty: The geo-replication session has witnessed some abnormality and the situation has to be investigated further. For further information, see section. Corrupt: The monitor thread which is monitoring the geo-replication session has died. This situation should not occur normally, if it persists contact Red Hat Support.

To configure Gluster Geo-replication Use the following command at the Gluster command line: # gluster volume geo-replication MASTER SLAVE config [options] For more information about the options, see . For example: To view list of all option/value pair, use the following command: # gluster volume geo-replication Volume1 example.com:/data/remote_dir config

You can use the gluster command to stop Gluster Geo-replication (syncing of data from Master to Slave) in your environment. To stop Gluster Geo-replication Stop geo-replication between the hosts using the following command: # gluster volume geo-replication MASTER SLAVE stop For example: # gluster volume geo-replication Volume1 example.com:/data/remote_dir stop Stopping geo-replication session between Volume1 and example.com:/data/remote_dir has been successful See for more information about the gluster command.

You can restore data from the slave to the master volume, whenever the master volume becomes faulty for reasons like hardware failure. The example in this section assumes that you are using the Master Volume (Volume1) with the following configuration: machine1# gluster volume info Type: Distribute Status: Started Number of Bricks: 2 Transport-type: tcp Bricks: Brick1: machine1:/export/dir16 Brick2: machine2:/export/dir16 Options Reconfigured: geo-replication.indexing: on The data is syncing from master volume (Volume1) to slave directory (example.com:/data/remote_dir). To view the status of this geo-replication session run the following command on Master: # gluster volume geo-replication Volume1 root@example.com:/data/remote_dir status MASTER SLAVE STATUS ______ ______________________________ ____________ Volume1 root@example.com:/data/remote_dir OK Before Failure Assume that the Master volume had 100 files and was mounted at /mnt/gluster on one of the client machines (client). Run the following command on Client machine to view the list of files: client# ls /mnt/gluster | wc –l 100 The slave directory (example.com) will have same data as in the master volume and same can be viewed by running the following command on slave: example.com# ls /data/remote_dir/ | wc –l 100 After Failure If one of the bricks (machine2) fails, then the status of Geo-replication session is changed from "OK" to "Faulty". To view the status of this geo-replication session run the following command on Master: # gluster volume geo-replication Volume1 root@example.com:/data/remote_dir status MASTER SLAVE STATUS ______ ______________________________ ____________ Volume1 root@example.com:/data/remote_dir Faulty Machine2 is failed and now you can see discrepancy in number of files between master and slave. Few files will be missing from the master volume but they will be available only on slave as shown below. Run the following command on Client: client # ls /mnt/gluster | wc –l 52 Run the following command on slave (example.com): Example.com# # ls /data/remote_dir/ | wc –l 100 To restore data from the slave machine Stop all Master's geo-replication sessions using the following command: # gluster volume geo-replication MASTER SLAVE stop For example: machine1# gluster volume geo-replication Volume1 example.com:/data/remote_dir stop Stopping geo-replication session between Volume1 & example.com:/data/remote_dir has been successful Repeat # gluster volume geo-replication MASTER SLAVE stop command on all active geo-replication sessions of master volume. Replace the faulty brick in the master by using the following command: # gluster volume replace-brick VOLNAME BRICK NEW-BRICK start For example: machine1# gluster volume replace-brick Volume1 machine2:/export/dir16 machine3:/export/dir16 start Replace-brick started successfully Commit the migration of data using the following command: # gluster volume replace-brick VOLNAME BRICK NEW-BRICK commit force For example: machine1# gluster volume replace-brick Volume1 machine2:/export/dir16 machine3:/export/dir16 commit force Replace-brick commit successful Verify the migration of brick by viewing the volume info using the following command: # gluster volume info VOLNAME For example: machine1# gluster volume info Volume Name: Volume1 Type: Distribute Status: Started Number of Bricks: 2 Transport-type: tcp Bricks: Brick1: machine1:/export/dir16 Brick2: machine3:/export/dir16 Options Reconfigured: geo-replication.indexing: on Run rsync command manually to sync data from slave to master volume's client (mount point). For example: example.com# rsync -PavhS --xattrs --ignore-existing /data/remote_dir/ client:/mnt/gluster Verify that the data is synced by using the following command: On master volume, run the following command: Client # ls | wc –l 100 On the Slave run the following command: example.com# ls /data/remote_dir/ | wc –l 100 Now Master volume and Slave directory is synced. Restart geo-replication session from master to slave using the following command: # gluster volume geo-replication MASTER SLAVE start For example: machine1# gluster volume geo-replication Volume1 example.com:/data/remote_dir start Starting geo-replication session between Volume1 & example.com:/data/remote_dir has been successful

Manually Setting Time If you have to change the time on your bricks manually, then you must set uniform time on all bricks. This avoids the out-of-time sync issue described in . Setting time backward corrupts the geo-replication index, so the recommended way to set the time manually is: Stop geo-replication between the master and slave using the following command: # gluster volume geo-replication MASTER SLAVE stop Stop the geo-replication indexing using the following command: # gluster volume set MASTER geo-replication.indexing off Set uniform time on all bricks.s Restart your geo-replication sessions by using the following command: # gluster volume geo-replication MASTER SLAVE start Running Geo-replication commands in one system It is advisable to run the geo-replication commands in one of the bricks in the trusted storage pool. This is because, the log files for the geo-replication session would be stored in the *Server* where the Geo-replication start is initiated. Hence it would be easier to locate the log-files when required. Isolation Geo-replication slave operation is not sandboxed as of now and is ran as a privileged service. So for the security reason, it is advised to create a sandbox environment (dedicated machine / dedicated virtual machine / chroot/container type solution) by the administrator to run the geo-replication slave in it. Enhancement in this regard will be available in follow-up minor release.