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Introduction

 

Not unlike Network Management Systems (NMS), Data Center Infrastructure Management (DCIM) software also monitors diverse set of equipment. The equipment ranges from server, network switches, Power Distribution Units (PDUs), panels, sensors, Diesel Generator (DG) sets. These devices have different protocols – MODBUS, SNMP, and BACNET. In addition, the parameters, that are monitored, are also different. For example the monitored parameters from a DG set may be output voltage, output power, and output current for all phases. Now in the case of a sensor it may be temperature and relative humidity.  The software needs to capture the data from the various devices, keep in persistent store and report/alert on the data. This poses a problem if we want to store in traditional row/column format of relational data base. We will explore the implementation options and the method adopted.

 

Implementation Options in RDBMS

 

If we choose to store the monitored data in traditional relational form we have couple of options:

 

  1. Build a super set of column list from all the monitored devices

    If we choose this option then let’s say that we have 3 devices A, B & C and for A the monitored parameters are x, y, for B the monitored parameters are y, z, and for C the monitored parameters are x, z. So if we have a table with columns x, y and z it should suffice. Well in the real world the number of devices can run into hundreds of types with each device having multiple unique parameters. In that case you will see that the number of columns will easily run into few hundreds making the table design unwieldy. Furthermore, when it is populated with data it will be sparse. Of course, every time a new device is added with unique parameter, one will have to add columns to the table making the design untenable.

  2. Have a table per device

    This approach is somewhat better than the previous one - in the design add a table, which is unique to the type of device. For example there will be a table for DG set with columns for parameters that are monitored for a DG set, a table for a sensor with temperature and relative humidity as columns, so on and so forth. It sounds logical. However, this design also suffers from similar deficiencies as stated above. Let us say you have 2 DG sets from two different manufacturers and their monitored parameters, although having overlaps, are not exactly same. So what do we have to do – add two different tables for 2 DG sets? There goes the design principle for a toss!

 

How to retrofit in a RDBMS based solution?

 

Having described the issues that we encountered, how do we design the persistence of monitored data? The natural choice would have been NOSQL databases such as Cassandra or similar persistent store. The NOSQL data model is a dynamic schema, column-oriented data model. This means that, unlike a relational database, you do not need to model all of the columns required by your application up front, as each row is not required to have the same set of columns. Columns and their metadata can be added by your application as they are needed without incurring downtime to your application.Since we had to retrofit the design into an already existing relational schema, we chose have a single column of text (varchar field in RDBMS terminology) sufficiently large to hold the monitored data. However, we devised a scheme such that when we acquire data we say what field it is, what is the unit and what is the value. For example if from a sensor we acquire temperature and relative humidity, the data that is written into the table will be “field = temp, unit = Celsius, value = 22/field = RH, unit = %, value = 50”. Similarly for a generator a data row may be “field = voltage, unit = volt, value = 240/field = power, unit = KW, value = 100”. Both these data points will go into the same column and another column for their unique device id. Having done this we simplified the design, its maintenance and reporting. A separate reporting module which normalizes the data after suitably extracting from the monitored table suffices to do all kind of reporting from each unique device. It is flexible enough to add new devices with its own unique parameters without changing the core tables. This is how we married structure and unstructured data.

 

Published in DCIM

What does one want to see in a data center layout?

 

When one sees a geographical map of a city, one is interested in the streets, the buildings, the parks, commercial establishments, houses etc. Similarly when a data center operator sees a data center layout he/she is interested in the aisles: 1) Cold aisle – the cool air is blown to the racks from this aisle 2) Rack aisle – a row where racks are placed 3) hot aisle – aisle on the back side of rack where the hot air comes out. In addition to the aisles there are a number of other equipment that are seen in the data centers such as 1) Precision Air Conditioners (PACs) 2) Power Distribution Units ( PDUs) 3) Panels. By looking at a data center layout diagram one must know the current state of the layout – where each asset is, how much is utilized?

Hence broadly the requirements for data center layout are:

1) To depict the aisles - hot, cold and rack aisles

2) To show the equipment on the floor - PDUs, Panels,, PACs

3) To show walls separating adjacent rooms

4) To show entry/exit doors

5) To be able to add/move/delete assets such as Racks, PDUs, Panels, sensors.

Implementation methodology & technology choice

The model and visualization  implementation choices are many. The obvious choice is to use Java technologies such as Javascript and JSP. However, it is ideal to separate the model from visualization. Let us take couple of examples to drive home the point. When we describe a circle it is sufficient to say where the center is and the size of the radius. Now how we draw the circle on the screen is a separate task. Similarly when we describe a room, if we specify its coordinates and which corner some furniture is placed we can form an idea of the room even before it is shown to us pictorially. It is universally accepted principle in computing that model (or data) is separated from the algorithm which deals with the data. If we have a text file which describes the data center and if the text file can be easily edited by hand or program, the code becomes much more flexible to extend and maintain. With that goal in mind we set out to choose the best implementation choice for data center layout. GFS accomplished this separation by using XML, XSLT technologies.  We were also able to overlay the assets with real time monitored data for the assets.The solution is extensible, flexible and can be customized for a particular data center. Yes we did actually customize it for a diesel generator enclosure showing DG sets, buffer tanks, flow meters vindicating that XML, XSLT is the right choice for modelling and visualization of data center layout.


 

 

 

 

 

 

 

 

Published in DCIM

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