[Info-vax] OpenVMS - file selection abnormally with Copy / Rename or user ignorance?

[Stephen Hoffman]

TL;DR:  BACKUP /IGNORE=INTERLOCK is not an entirely reliable online 
backup mechanism.

On 2015-03-29 01:44:07 +0000, JF Mezei said:

> Are there cases where BACKUP/IGNORE would NOT report a file as 
> currently opened at the time BACKUP begins to copy a file ?

That would be the "silent" part, yes.

> And in terms of problems, instead of "corruption" isn't it more correct 
> to state "unpredictable data" ?

"Data corruption refers to errors in computer data that occur during 
writing, reading, storage, transmission, or processing, which introduce 
unintended changes to the original data."

In short: Toh-may-toh, Toh-mah-toh

Why BACKUP /IGNORE=INTERLOCK is a problem involves a trip through the 
basics of file locking and that might be interesting to some, and the 
general locking details are in the various Internals and Data 
Structures books  and in the VMS File Systems Internals book, and the 
shorter version of the answer is in that Note from the OpenVMS 
documentation that was posted earlier.

Now having a reliable online BACKUP mechanism for RMS files — which 
would likely involve application integration and/or use of RMS 
Journaling — would be far more interesting.   For new applications and 
for applications that are getting overhauled, it's usually easier to 
use a database package that provides online backup support.  Both of 
which are part of my usual list of "it would be nice..." features for 
integration into the base OpenVMS distribution.

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