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RawDisk - locked files backup

Posted: 03/17/2009 16:52:49
by stephane  (Standard support level)
Joined: 03/17/2009
Posts: 39


Is it possible with Rawdisk to perform file "snapshots" (that is read a locked file in consistent state to backup it , and let at the same time the application that locked it continue to write to the file) ?

An example could be a database file, the database engine must be able to continue inserting/updating data while my backup app is reading the file in the state it was when I started reading it. (else I will often backup inconsistent data and that would be useless to restore it).

If this is not supported as a standard, is there a simple way to do this with Rawdisk ?
Posted: 03/18/2009 05:33:23
by Volodymyr Zinin (Team)


I will see what it is possible to do and answer a little later.
Posted: 03/19/2009 01:37:19
by Volodymyr Zinin (Team)

Unfortunately it isn't possible to do using RawDisk.
Posted: 03/19/2009 02:14:07
by Eugene Mayevski (Team)

I'd say that it's contrary to the common sense as well. In general if the file is opened for writing, you can't be sure that it's in consistent state at any given moment of time. It's possible that the application has written only half of the data (thus keeping the state inconsistent) and paused writing for some reason. Now you start copying the data from the file. It's not important whether the application starts writing anything again or it stays paused. You will grab the data in inconsistent state anyway. That's the risk of copying the open file that you or the user must take.

Sincerely yours
Eugene Mayevski
Posted: 03/19/2009 03:57:33
by stephane  (Standard support level)
Joined: 03/17/2009
Posts: 39

Thanks for your answers :)

Eugene in theory you are right, there is no way to be sure that application hasn't paused writing (crash, waiting some external event ...), but in practice applications try to maintain as much as possible they datafiles in consistent state.

What I want is just to minimize the probability of saving a big file with inconsistent data "just because reading it takes a large amount of time" (I can't do nothing against other external reasons so I want to at least control this one).
Using snapshots (temporary file stream redirection) solves this issue.

Posted: 03/19/2009 04:19:50
by Eugene Mayevski (Team)

I think it's possible to do capturing of the data being written using CallbackFilter and it's more suitable tool to do the job.

Sincerely yours
Eugene Mayevski



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