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Visual Foxpro Backup

Posted on 2010-08-31
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Hello Experts,

I am setting up shadowprotect backup (vss snapshot based whole disk backup) for a client on their Foxpro server and I am unclear if we still need to follow our old backup procedure which was to manually do a "cold backup" from the medical database application (written in FoxPro). The application has a "backup" item under the "File" menu which requires that all users be out of the application first. Since the new backup software utilizes VSS, do we still need to follow the "cold" backup procedure?

Thanks very much!
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Question by:JohnnyD74
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Expert Comment

by:Tomas Valenta
ID: 33574326
Always is better to have two backups of data on separated media (Tape + external HDD) and it could be also backups made by two applications. Database must have support for backing up by VSS snapshots - it is better to find it in documentation.
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Accepted Solution

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Olaf Doschke earned 2000 total points
ID: 33574459
VSS is doing shadow copies for any file, also foxpro data. Still when working on data, and SQL Server MDF files are no difference to this, there are many concurrent changes and in a multi user system users have changes in buffers, which are local.

VSS does no overall snapshot of all the files on a volume, a backup can take the "snapshot" of the most current shadow copy of a file, but that can change during backup, as a foxpro database is not a single file and even a single table can have two or three files.

The cold backup assures you have a good data integrity.

Besies that for bigger dbfs, where you have changes with each new record or each record change, you will have many shadow copies of the same file and I wonder if that works well if table sizes reach several MBs to create an accurate shadow copy will mean copying several MBs for each single record change or at least for each transaction, if the app uses transactions.

You're on the sure side doing the cold backup.

Bye, Olaf.
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Assisted Solution

by:Olaf Doschke
Olaf Doschke earned 2000 total points
ID: 33574518
to clarify:

In what SQL Server MDF files do not differ is, that users don't work on databases as on office documents, you don't open a file and edit it, you retrieve records of tables, small portions, edit them in a form and the commit changes. This can be done transaction for transaction, encapsulating changes to many tables which only result in integral, wholesome data, if the changes are all done or none of them is done.

Without transactions encapsulating changes this way a database can be in a non integral state during saving many changes. But even with transaction you loose the last changes not yet committed when doing a hot backup.

You might say that's not much, every user could reapply the changes made after a restore of the data, but users might not remember what they did the last time before a database crash. Or they might not notice something missing. For example if you have a recipe for some medicine and this is stored with a main record and several records with the ingredients, what might be backed up when the backup occurs while saving a recipe is only part of a recipe with some ingredients missing. Especially if there is not a transactional saving of whole recipes, which would use exclusive access to both recipes and ingredients table, so even VSS service could only do a shadow copy of a wholesome recipe.

If the foxpro app does use transactions the damage to the integrity of data could be prevented. Nevertheless, this needs to have been programmed this way, it's not automatically this way and a transaction log also is no mechanism of foxpro databases.

Bye, Olaf.
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Author Closing Comment

by:JohnnyD74
ID: 33579532
Thank you so very much Olaf! We will continue the "cold" backup!
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