multi xfs support

[Assar Westerlund]

Marek Kowal <tomcat at fatcat.desy.de> writes:
> Well, as usual, the whole thing is in our heads ;-) 
> 
> RFIO stands for Remote File Input/Output.  You might try to see the
> quite-outdated version of it on
> http://wwwinfo.cern.ch/pdp/serv/SHIFT_1.10.3.5_SRC.TAR.gz, or the newer
> one in: http://wwwinfo.cern.ch/pdp/castor/.

With some quick surfing, I failed to find documentation on RFIO there,
but I might be looking in the wrong place.

> Anyway, not to create to much
> fuss, RFIO library is just a set of calls that behave in EXACTLY the same
> way as standard C library IO calls, that is: open, close, read, write,
> lseek and so on.

ok

> Unfrotunately this works only for C programs, and not for the
> Fortran, which is widely used here at DESY. This is why we need
> filesystem.

Another way that should, I think, work fine for fortran too is to use
a shared library that implements these functions?

> Do you think it would be easy to implement forwarding of data read/write
> calls from xfs to my daemon as well? 

That would require some changing, but it should not be especially
difficult.

> On the other hand, I would not mind against caching the data by
> local filesystem, but only the data that were requested by
> read/write.

Yeah, just caching blocks of a file is on out TODO-list.  And this
would probably be the simplest way.

> Unfortunately, as far as I understood, you fetch the whole file to the
> local cache upon opening it... do you think, btw, that this is wise?
> Wouldn't it be better to have arlad operating on "blocks", that is
> fragmetns of files? They would be requested upon read/write, and of course
> cached locally for bigger performance.

Right.  We mostly cache whole files for simplicity.

> ps. could you add me to the mailing list, please?

Just send "subscribe" in the body of a mail to
<arla-drinkers-request at stacken.kth.se> and you should get added
automatically.

/assar