Hi Volodymyr ,
Hmmm, seems that when I go down this path, there appears to be a disconnect
between the SRM and a data access system concepts. What xrootd provides to
clients is low latency high performance random access on par with the best
commercial systems out there. That can't be done with the SRM protocol
(i.e., delivering random access data to client analysis jobs). On the other
hand, xrootd relies on some other entity to manage the disk cache. All that
xrootd requires is physical access to that cache and some amount of
predictability in its management (though it's reselient to crazed
management). To date, xrootd interfaces to the mps system which can be
customized to talk to a general purpose MSS (it can actually talk to an
SRM/DRM combination as well if you don't mind double caching).
The general integration of SRM calls for using SRM facilities to bring files
into some disk cache when needed. Access to data in those files uses either
the root framework or the Posix calls (which in turn use the xrootd). Where
that fits in depends on what whether the SRM implementation provides some
disk cache management features or not. So, from an SE perspective, the SE
provides an SRM interface to the outside world but internally provides
xrootd access to applications.
Andy
----- Original Message -----
From: "Volodymyr Kapchynskyy" <[log in to unmask]>
To: "Andy Hanushevsky" <[log in to unmask]>; <[log in to unmask]>;
"Patrick Fuhrmann" <[log in to unmask]>
Sent: Monday, September 19, 2005 1:28 AM
Subject: Re: dCache wants to communicate with XRootd
>
> Hi Andy,
>
> Thanks for the detailed reply.
> We will make ourselves familiar with the descriped
> mechanisms.
> There is just some question left about integrating
> SRM into the xrootd service.
> Did I understand correctly that
> "to integrate xrootd with a generalized SRM" means that
> instead of having oss/ofs and/or MPS you would prefer to talk
> SRM client protocol and with that have a general interface
> to mass storage systems (disk/tape) ?
> BTW: are there any plans to let xrootd talk the SRM
> server protocol so that it can serve as a Storage Element ?
>
> dCache Team
>
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