dynamo-consistency

.. _intro-ref:

Introduction

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Dynamo Consistency is the consistency plugin for Dynamo Dynamic Data Management System. Even though Dynamo controls and tracks the history of file transfers between computing sites, a separate check is needed to ensure files are not lost or accumulated during user or system errors. Sites that can no longer access files after a power outage, for example, can cause other problems for the entire data management system. Transfers requested from the site to another site will fail for missing files. Sites are chosen incorrectly for production jobs that assume the presence of a local file. Last disk copies may also be missing, causing a delay for user requests for data. Another type of inconsistency is caused when files thought to be deleted are still on disk. This leads to wasted disk space for files that are not accessed, except by accident. Dynamo Consistency does its check by regularly listing each remote site and comparing the listed contents to Dynamo's inventory database.

The package also includes a number of modules that can be imported independently to create custom consistency check runs. A simple consistency check on a site can be done by doing the following when an instance of dynamo is installed::

from dynamo_consistency import config, datatypes, remotelister, inventorylister

config.LOCATION = '/path/to/config.json' site = 'T2_US_MIT' # For example

inventory_listing = inventorylister.listing(site) remote_listing = remotelister.listing(site)

datatypes.compare(inventory_listing, remote_listing, 'results')

In this example, the list of file LFNs in the inventory and not at the site will be in results_missing.txt. The list of file LFNs at the site and not in the inventory will be in results_orphan.txt. The listing functions can be re-implemented to perform the check desired.

Installation ++++++++++++

Dynamo Consistency requires the XRootD <http://xrootd.org/doc/python/xrootd-python-0.1.0/>_ Python module to be installed separately. In addition, it uses the Dynamo Dynamic Data Management package to get inventory listings and to report results of the consistency check. Any other needed packages are installed with Dynamo Consistency during installation.

The simplest way to install is through pip::

pip install dynamo-consistency

The source code is maintained on GitHub <https://github.com/SmartDataProjects/dynamo-consistency>_. Other typical setuptools methods are supported by the repository's setup.py.

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