MediFile Mirror Backup

Date of Tech Note: 26 July 1999
Enhancement: 26 July 1999
Bug Fix: N/A

Description

At larger sites, MediFIle is setup to have the a very high degree of backup. This document briefly describes the backup strategies employed with MediFile, and how to configure them.

Details

In a brief format here is the various backup strategies that are used at these sites (all are installed).

1. - RAID level 5 drives on Main Server

When anything is written by the main server to the hard drives it is written in two places. Therefore if a hard drive dies, the system still operates without the loss of data.

When a hard drive dies, while the system is still running, it can be removed and a new hard drive installed.

2. - Mirror Data Base

There are essentially three tasks that a server computer does that modifies the data on the server.
1 - Add a new record
2 - Modify a record
3 - Delete a record

With this configuration, every time one of the changes indicated above occurs, the 4th Dimension server writes the change to the data base and writes the changes to a log file. This log file is essentially a large text file with each of the changes written in sequential order. Once every hour the log file is sent to the mirror database.

On a second server 4D Backup is running. The second server has a complete copy of the MediFile program, and the data file from the last backup. When the log file is sent to the second server the 4D Backup application reads the log file and updates its data file with all the changes indicated in the log file that was sent.

So at the end of the update process, the mirror data base is up to date with the main server (except for the transactions that occurred since receiving the log file)

3. - Off Site Tape Backup

Every week night a complete copy of the data file is written to tape. The tape is then removed by a person and taken off site. A new tape is put into the tape drive for the next nightly backup.

The three levels of backup provide for the maximum security of data as well as for varying speed of recovery. The speed of recovery is the fastest for #1 then #2, and then #3. Additonally the least amount of data loss occurs with #1 (should be none), then 2 and then 3.

Data Loss should Backup be Needed

1. RAID Level 5 ( incase a hard drive on the main system fails)

No data loss if only one drive dies. This is because everything is written in two places at exactly the same time. Since this is at the time that the data is written for the first time, it will always be here first. If one drive dies the system automatically and instantly (as far as the human eye is concerned) adjusts and gets the data from the other area.

2. Mirror Backup ( incase the main server becomes inoperable for any reason)

No data loss if the latest log file is integrated. We set up the log file to be integrated 1 time per hour. Therefore the oldest that this data file will be is one hour. Should the main server die and you have the latest log file, you can integrate it. Since all transactions are written to the log file at the same time they are written to the RAID drives on the main server, no data should be lost at this time.

The Mirror backup needs to have the latest log file integrated before it is ready to be used. The process of integration could take a couple of minutes for maybe 10 minutes. It will depend on the amount of data that was added, deleted, or modified.

Once the log file is integrated, the 4D Backup application is quit, and 4D Server launched to use the MediFile program and data stored on the backup computer. This whole process may take as little as 5 minutes from the time it is decided that you need to use the mirror data base.

3. Tape Backup (if both servers died, were stolen, or you had a fire)

The longest step for this is likely to be getting the tape from the off site storage area. Once you have the tape, you need to go through the restore process with the tape backup software you purchased. The time for this depends on your hardware, backup software, and the size of your data file. Expect that it will take twice as long to restore as it does to perform the backup. With a one gig data file it may take about 20 minutes to backup the data file with some configuration. Therefore it would take about 40 minutes plus tape retrival time to get MediFile backup and running.

Step One

Initial Setup of MediFile Server

You need to tell the MediFile server computer to use a log file. You do this by clicking on ‘Select Log File’ in the File menu.

When this has been set up correctly the MediFile Server will show that you have a log file being generated. This is seen as shown here.

Where the arrow is pointing in the diagram you can see Log: F:\Peterborough.4DL

This indicates that the log file is being written to the F Drive with a name of Peterborough.4DL

We will need to come back to the MediFile server for more setup once we have the mirror computer setup.

Setting up the Mirror Data Base

The mirror data base is contained on the secondary MediFile server. This is the server computer located in the middle of the DELL computers sitting on the bottom row of the server rack.

The TCP/IP address for this computer is 192.168.0.3.

The Data Base and 4D backup is located on the E drive.

Double click on the E volume and then once inside there double click on the E Mirror directory (folder). This wil bring you to the location of the 4D Backup and MediFile program.

In this diagram the MediFile program is called MediFile25Ju... To see the full name you select the View menu and select list. This will give you a view with the full name of the files.

In this case the MediFile Program has a name of MediFile25July.4DC. It is absolutely critical that this version be exactly the same as the verion of MediFile on the main server. The mirror will not work at all if it is a different version.

Double click on the 4D Backup.exe file. This will launch 4D Backup.

Click on the Mirror button in the 4D Backup dialog.

This will launch the mirroring function of 4D Backup.

4D Backup will ask you to select the MediFile structure for it to use. This will be in a standard file dialog box.
By default it looks for an uncompiled structure (.4db).

We need to tell 4D Backup to look for a compiled structure (.4DC). Do this by selecting it in the List files type popdown.

The compiled MediFile Structure will then be displayed in the File selection list. Click on it, and click on the OK button.

Enter the Administration name & password as if you were signing into MediFile.

When you have sucessfully entered the administration name and password the 4D Backup Mirror dialog will be shown.

We need to set the preferences for the MediFile Mirror. Do this through the Preferences menu item in the File menu.

In the preferences set them as shown here.

Save these preferences.

Under the File menu you can select Save As if this mirror project has not already been saved. Most likely you will just have been opening up the project and it will be preconfigured for you.

Return to The MediFile Server

You need to go to the Main MediFile Server computer now.

In the Backup Menu you need to select ‘Update Mirror’. When you select this MediFile will ask you to select the Mirror data base to send the log file to. The Mirror data base will show up in the selection dialog box similar to a log on dialog.

Click on the MediFile that is shown here. It will only show mirror MediFiles.

The Update Mirror configuration dialog will be shown.

The only parameter that needs to be changed is the ‘Number of sets’. set this to None by clicking on the down arrow button beside it until it says none.

Click on the Send log button.

You will now see a dialog showing the progress of the sending of the log file. The MediFile server is now sending the log file to the backup server. It will also have created a new log file.

You now need to save the Update Mirror paramaters. The MediFile server will ask you to do this automatically.

Save them with the main MediFile Server application.

The MediFile server will go back to its regualar appearance.

You now need to set up the MediFile server to automatically update the mirror data base. Do this by selecing 1 hour in the mirror dialog. Then click on the checkbox.

If you were to watch the Mirror data base server after a log file has been sent you would see the following dialog. This dialog indicates that it is integrating all the changes from the log into its data file.

Once it has integrated the log file it will go back to the regular ‘Mirror’ dialog.