.. _guide-101-simplestorage:

Creating a simple storage service
=================================

.. _guide-simplestorage-overview:

Overview
========

A Simple storage service is the simplest possible abstraction for a
service that can store and provide access to workflow files. It has a
certain storage capacity, and provides write, read, and delete
operations on files. In addition, higher-level semantics such as copying
a file directly from a storage service to another are provided.

.. _guide-simplestorage-creating:

Creating a Simple storage service
=================================

In WRENCH, a Simple storage service represents a storage service
(:cpp:class:`wrench::StorageService`), which is defined by the
:cpp:class:`wrench::SimpleStorage` class. An instantiation of a Simple storage
service requires the following parameters:

-  The name of a host on which to start the service;
-  A list of mount points (corresponding to disks attached to the host);
   and
-  Maps (``std::map``) of configurable properties
   (:cpp:class:`wrench::SimpleStorageServiceProperty`) and configurable message
   payloads (:cpp:class:`wrench::SimpleStorageServiceMessagePayload`).

The example below creates an instance of a Simple storage service that
runs on host ``BigDisk``, has access to the disks mounted at paths
``/data/`` and ``/home/`` at host ``BigDisk``. Furthermore, the number
of maximum concurrent data connections supported by the service is
configured to be 8, and the message sent to the service to find out its
free space is configured to be 1KiB:

.. code:: cpp

   auto storage_service = simulation->add(
             new wrench::SimpleStorageService("BigDisk", 
                                     {"/data/", "/home/"},
                                          {{wrench::SimpleStorageProperty::MAX_NUM_CONCURRENT_DATA_CONNECTIONS, "8"}},
                                          {{wrench::SimpleStorageServiceMessagePayload::FREE_SPACE_REQUEST_MESSAGE_PAYLOAD, "1024"}
                                         );

See the documentation of :cpp:class:`wrench::SimpleStorageServiceProperty` and
:cpp:class:`wrench::SimpleStorageServiceMessagePayload` for all possible
configuration options.

Also see the simulators in the ``examples/basic-examples/*``
directories, which all use simple storage services.