Re: file position on tape

[Arie Shoshani <arie@math.lbl.gov>]

> Dave Z. and I spoke with John Riordan (and Ed and Razvan) yesterday
> about getting information of where files are on tape.
> The thing that looks like it should be easy to do is to
> get the list, for a class of service (COS), of 
> filenames, tape number, and position (order) of file on tape.
> I was thinking that you could use this along with the
> list of files that go into the GC index to include the
> information about tape number and order on tape.
> Then it would be possible (conceptually) to include this
> tape information in the policy decisions about what
> order to retrieve files.
> Dave will be back at LBL on Thursday and can talk to you
> about it, and probably show you an example of a file that
> has the tape information.  If you recall, he got information
> like that about the files we used at the end of MDC1.
> Why don't you think about that and consider whether it
> is possible to use it in MDC2.
> 
> Thanks,
> Doug

Doug,

That can be very useful information, so we should try to make it available
in the index.  But, as Alex said any policies that use tape information
should be left to be done after MDC2.

BTW, taking advantage of tape information is partially done by HPSS if we
request sufficient number of PFTPs.  If many PFTPs are in the HPSS queue it
optimizes the order of reading them.

Arie.