relation between NSF and NSF.DATA

Hi,

So far I have failed to find an explanation what exactly NSF and NSF.DATA files are.

It seems that *NSF is kind of reference and actual data are stored as *NSF.DATA.

My first question would be: is there 1:1 relation between those files?

Because on our TSM server the number of NSF files matches number of NSF.DATA files only for inactive backups, but when talking only about active versions, we have more *NSF then *NSF.DATA files. Is it all right? How can it be explained?

Also we have some very old NSF files, that do not have corresponding NSF.DATA files (at least not of the same backup date)...

So I am bit confused, and would welcome any advice.

Thanks