Preparing and Adding Hosts

Adding New Hosts to the Trusted Host Environment
Validating Disk I/O and Memory Bandwidth
- To run gpcheckperf
Integrating New Hardware into the System

Verify your new host systems are ready for integration into the existing LightDB-A system.

To prepare new host systems for expansion, install the LightDB-A Database software binaries, exchange the required SSH keys, and run performance tests.

Run performance tests first on the new hosts and then all hosts. Run the tests on all hosts with the system offline so user activity does not distort results.

Generally, you should run performance tests when an administrator modifies host networking or other special conditions in the system. For example, if you will run the expanded system on two network clusters, run tests on each cluster.

Note Preparing host systems for use by a LightDB-A Database system assumes that the new hosts’ operating system has been properly configured to match the existing hosts, described in Configuring Your Systems.

Parent topic: Expanding a LightDB-A System

Adding New Hosts to the Trusted Host Environment

New hosts must exchange SSH keys with the existing hosts to enable LightDB-A administrative utilities to connect to all segments without a password prompt. Perform the key exchange process twice with the gpssh-exkeys utility.

First perform the process as root, for administration convenience, and then as the user gpadmin, for management utilities. Perform the following tasks in order:

To exchange SSH keys as root
To create the gpadmin user
To exchange SSH keys as the gpadmin user

Note The LightDB-A Database segment host naming convention is sdwN where sdw is a prefix and N is an integer ( sdw1, sdw2 and so on). For hosts with multiple interfaces, the convention is to append a dash (-) and number to the host name. For example, sdw1-1 and sdw1-2 are the two interface names for host sdw1.

To exchange SSH keys as root

Create a host file with the existing host names in your array and a separate host file with the new expansion host names. For existing hosts, you can use the same host file used to set up SSH keys in the system. In the files, list all hosts (coordinator, backup coordinator, and segment hosts) with one name per line and no extra lines or spaces. Exchange SSH keys using the configured host names for a given host if you use a multi-NIC configuration. In this example, cdw is configured with a single NIC, and sdw1, sdw2, and sdw3 are configured with 4 NICs:
```
cdw
sdw1-1
sdw1-2
sdw1-3
sdw1-4
sdw2-1
sdw2-2
sdw2-3
sdw2-4
sdw3-1
sdw3-2
sdw3-3
sdw3-4
```
Log in as root on the coordinator host, and source the lightdb_a_path.sh file from your LightDB-A installation.
```
$ su - 
# source /usr/local/greenplum-db/lightdb_a_path.sh
```

Run the gpssh-exkeys utility referencing the host list files. For example:

# gpssh-exkeys -e /home/gpadmin/<existing_hosts_file> -x 
/home/gpadmin/<new_hosts_file>

gpssh-exkeys checks the remote hosts and performs the key exchange between all hosts. Enter the root user password when prompted. For example:
```
***Enter password for root@<hostname>: <root_password>
```

To create the gpadmin user

Use gpssh to create the gpadmin user on all the new segment hosts (if it does not exist already). Use the list of new hosts you created for the key exchange. For example:
```
# gpssh -f <new_hosts_file> '/usr/sbin/useradd gpadmin -d 
/home/gpadmin -s /bin/bash'
```
Set a password for the new gpadmin user. On Linux, you can do this on all segment hosts simultaneously using gpssh. For example:
```
# gpssh -f <new_hosts_file> 'echo <gpadmin_password> | passwd 
gpadmin --stdin'
```
Verify the gpadmin user has been created by looking for its home directory:
```
# gpssh -f <new_hosts_file> ls -l /home
```

To exchange SSH keys as the gpadmin user

Log in as gpadmin and run the gpssh-exkeys utility referencing the host list files. For example:
```
# gpssh-exkeys -e /home/gpadmin/<existing_hosts_file> -x 
/home/gpadmin/<new_hosts_file>
```
gpssh-exkeys will check the remote hosts and perform the key exchange between all hosts. Enter the gpadmin user password when prompted. For example:
```
***Enter password for gpadmin@<hostname>: <gpadmin_password>
```

Validating Disk I/O and Memory Bandwidth

Use the gpcheckperf utility to test disk I/O and memory bandwidth.

To run gpcheckperf

Run the gpcheckperf utility using the host file for new hosts. Use the -d option to specify the file systems you want to test on each host. You must have write access to these directories. For example:
```
$ gpcheckperf -f <new_hosts_file> -d /data1 -d /data2 -v 
```
The utility may take a long time to perform the tests because it is copying very large files between the hosts. When it is finished, you will see the summary results for the Disk Write, Disk Read, and Stream tests.

For a network divided into subnets, repeat this procedure with a separate host file for each subnet.

Integrating New Hardware into the System

Before initializing the system with the new segments, shut down the system with gpstop to prevent user activity from skewing performance test results. Then, repeat the performance tests using host files that include all hosts, existing and new.