To force usage of a specific key, put in your ~/.ssh/config file :

Host [HOST_NAME]
   Hostname [HOST_NAME]
   User [USER_NAME]
   Port [PORT]
   IdentityFile ~/.ssh/[your_private_key]

The apache benchmark tool is very basic, and while it will give you a solid idea of some performance.

Some parameters:

To get database table columns names of a mysql database you can use "DESCRIBE my_table;" method.

To create a bootable USB memory on linux you have several solutions. The famous dd is the most powerful solution, but use carefully. Because a very small error may destroy all your data.

Get, Set and Delete configuration value by drush

Get (drush config-get)

drush cget CONFIG_NAME CONFIG_KEY
Examples:
drush cget system.site
drush cget system.site page.front

Set (drush config-set)