Hi Volodymyr, For the posix access, how difficult would it be for dCache to expose its cache to xrootd (on the same servers) via a server-local soft link namespace to files on disk, for example? (Such a thing _does_ work as the Wisconsin people did this at one point to serve data in dCache via xrootd, although they had to create this server-local soft link namespace by hand.) Pete On Mon, Sep 19, 2005 at 04:26:50PM -0700, Andy Hanushevsky wrote: > 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 > > ------------------------------------------------------------------------- Peter Elmer E-mail: [log in to unmask] Phone: +41 (22) 767-4644 Address: CERN Division PPE, Bat. 32 2C-14, CH-1211 Geneva 23, Switzerland -------------------------------------------------------------------------