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WinCC Redundancy

Created by: Yolov at: 8/9/2006 2:13 PM (6 Replies)

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8/9/2006 2:13 PM	Rate (0)
Yolov Bronze Member Joined: 2/22/2006 Last visit: 1/7/2025 Posts: 291 Rating: (37)	Dear All, I want to ask you what is your opinion about WinCC database behaviour in ArchiveManager folder when Redundancy option is installed. For instance let assume that we have redundant WinCC couple. Both stations, OS1 and OS2 are running the runtime. Pretend we stop the RT on one of the WinCC stations (OS1 for instance) for commissioning, etc. Then we start the RT again. On the OS1 synchronization will take place. The missed data (Alarm Logging and Tag Logging Fast & Slow) for outage period will be preserved not into the last databases but into the new one. So we get new databases in ArchiveManager folder. I have to take care for redundant WinCC couple which I access through remote control software (NetOp). After 1 year of use the project folder is more than 2GB. When I inspect ArchiveManager\AlalrmLogging, ArchiveManager\TagLoggingFast and ArchiveManager\TagLoggingSlow I see tons of databases, some of them covered only a few hours. I will not comment the reasons of starting/stopping the RT on redundant couple. Important is the result. I don’t understand what is the problem the data for outage period to be preserved into the last database – as it is in stand-alone system? I ask the hot line if the WinCC developers will change the Redundancy behavior. They told me that they will not. I know that the WinCC developers are not fools and they have they own reasons to use this approach. Recently I work with Wonderware InTouch and the project with RT historian data are far below 1GB. My redundant couple backup the segments on another PC – long-term archiving (LAS) server running WinCC Dat@Monitor. I notice that the swapped out segments treat themselves in the same as way the databases in the ArchiveManager’s project folder. Here (on LAS) I get tons of databases some of them cover only a few hours!!! How to explain the client that he has to treat gigabytes of databases – some of them empty? I will not border you longer with my other favorite issue – WinCC Redundancy Option. I know that other colleagues are complaining that it is difficult to make it work. I have few years of experience and find more and more detail in contact of the hot line. Thank you in advance. Best regards, Svetozar Yolov

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8/10/2006 10:44 AM	Rate (0)
Salma Gold Member Joined: 9/27/2005 Last visit: 11/27/2007 Posts: 1398 Rating: (151)	My personal opinion is that WinCC Redundancy is a good option but only if it is used exactly as expected. Once you start to deviate from the developers vision you run into all kinds of problems. The first thing I would have to say is, seriously why is WinCC being stopped / started so often ?? This is not at all how it is expected to be operated and so the developers never envisaged the problem. This comes back to my above statement! Finally I can say that with V6 SP4, when a new database is created, the old database is closed AND shrunk. This means if it is empty then it will shrink down to a file size of 1Mb. This is much more usable for systems that have a large number of segments. Any chance you can upgrade to SP4 ?

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8/16/2006 4:51 PM	Rate (0)
Yolov Bronze Member Joined: 2/22/2006 Last visit: 1/7/2025 Posts: 291 Rating: (37)	Hi, many thanks for the answer. "Finally I can say that with V6 SP4, when a new database is created, the old database is closed AND shrunk. This means if it is empty then it will shrink down to a file size of 1Mb. This is much more usable for systems that have a large number of segments. Any chance you can upgrade to SP4 ?" The WinCC system are upgraded to WinCC v6.0 SP4. Could you explain me the behavior you mention above? Thanks a lot! Regards, Svetozar Yolov

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8/16/2006 5:10 PM	Rate (0)
Salma Gold Member Joined: 9/27/2005 Last visit: 11/27/2007 Posts: 1398 Rating: (151)	Sure. All SQLServer database files must have an initial size. Think of it like a bucket that needs to be filled with data. The bucket has a fixed size and it is the contents that vary. SQLServer is a little more sophisticated than a bucket [:P] and can increase the file size when it gets filled up. If the initialfilesize is set too small it can lead to bad performance as the database file grows and is fragmented. You can find a more detailed explanation of this process in Start -> Programs -> Microsoft SQL Server -> Books Online. From the WinCC Release Note for SP3 onwards ... "New individual segments take up half the storage space of the specified size for individual segments upon initial creation. For example, if you speficy the size of individual segments to be 1Gb, new segments will be created with a size of 500Mb each." ( NOTE: database file = segment ) However just because the database file is 500Mb in size, it does notnecessarily mean that it is using all that space. SQLServer has a SHRINK DATABASE facility that shrinks the file size to remove all unused space. So if a databaseonly contains ~5Mb of data, when a new database is created and the old one is closed and shrunk, it will go from 500Mb to 5Mb. I hope this makes sense. As you are already using SP4 I would expect you to see this behaviour already.
	Last edited by: salma at: 8/16/2006 5:23 PM Key thing is that if you do not set the "Size for all segments" and "Size of individual segments" correctly then you will get unnecessarily large database files.
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8/16/2006 5:29 PM	Rate (0)
Salma Gold Member Joined: 9/27/2005 Last visit: 11/27/2007 Posts: 1398 Rating: (151)	Also have you seen this FAQ http://support.automation.siemens.com/WW/view/en/22273427 New segments should not be created if you simply stop / start WinCC Runtime. It's only if you are making changes to the Alarm or Tag Logging Editors. If this is what you are doing constantly then maybe you should consider using an Engineering Station and using the Load Online Changes Editor to download changes to the server. Just a thought ...

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8/17/2006 3:14 PM	Rate (0)
Yolov Bronze Member Joined: 2/22/2006 Last visit: 1/7/2025 Posts: 291 Rating: (37)	Dear Salma, many thanks for the explanations. I want to clear just one issue. You said "Key thing is that if you do not set the "Size for all segments" and "Size of individual segments" correctly then you will get unnecessarily large database files." Of course the "Size for all segments" have to be multiplication of "Size of individual segments" and the number of segment choosen. Right? Or there is any other subtlety? What means that the sized have to be choosen correctly? Regards, Yolov

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8/18/2006 10:12 AM	Rate (0)
Salma Gold Member Joined: 9/27/2005 Last visit: 11/27/2007 Posts: 1398 Rating: (151)	You are correct about the "Size for all segments". It is obvious but still important [;)] When I say set the size correctly I mean not to make it too big. Let us assume we are logging 10 values every second. As you know, WinCC creates a new segment depending on either a size or a time limit, whichever occurs first. So for example, we can set the limits to100Mb and 1 week. One way to guarantee that the time limit is reached before the size limit is to increase the size limit to a very large value, e.g. 1Gb ! So we can be sure that a new segment is created every week and not every few days because we will never reach the maximum segment size of 1Gb. Although this will work it is lazy programming and as of SP3 it has a negative impact on the system. Our segments will be created with a size of 500Mb but they only need to store 6,048,000 values (number of values (10)x number of seconds in a day (86,400) x number of day in a week (7) ) ! However we only need ~90Mb ! This means that our segments are being created with an unnecessarily big size. This FAQhas thecalculation for determining segment sizes : http://support.automation.siemens.com/WW/view/en/22413908

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