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XROOTD-L  February 2005

XROOTD-L February 2005

Subject:

RE: How do we export multiple directories from xrootd.cf

From:

"Stephen J. Gowdy" <[log in to unmask]>

Reply-To:

Stephen J. Gowdy

Date:

27 Feb 2005 14:19:46 -0800 (PST)Sun, 27 Feb 2005 14:19:46 -0800 (PST)

Content-Type:

TEXT/PLAIN

Parts/Attachments:

Parts/Attachments

TEXT/PLAIN (102 lines)

Hi Matt,
	If there is no reason for NFS access you probably actually want a
set of xrootd servers and a redirector (or two), similar to BaBar's
Eventstore. The redirector is the first point of contact for all clients
and they then get told where the actual data is (all the servers tell the
redirector what they are willing to serve).

							regards,

							Stephen.

On Sun, 27 Feb 2005, Langston, Matthew David wrote:

> These things are great to know. We (GLAST) are just getting started with xrootd and have very little experience with setting it up properly to service the data handling needs of a Collaboration.
>
> I'll sketch out a little background of our use of xrootd so the xrootd community is at least aware of how we use xrootd and what are plans are for xrootd.
>
> We are building the GLAST data handling infrastructure based on a lightweight J2EE architecture. Our data handling applications will run in application servers in a distributed environment of multiple Linux and Windows servers.
>
> All of our data will reside in ROOT files stored on SLAC's NFS servers. Therefore, xrootd will initially be used to allow web applications running on both Linux and Windows a common point of (hopefully fast) access to these ROOT files. The only alternative for our Windows servers was to use NFS clients on Windows (which was discouraged by SCS), Samba (via \\slaccfs) which has been problematic), or making physically separate copies of the data for the Windows servers (which is obviously an unacceptable solution). Using xrootd servers seemed like a perfect solution.
>
> Currently, we use xrootd simply to allow our web applications to access the same set of root files stored in SLAC NFS space. For example, our System Tests web application at http://glast-ground.slac.stanford.edu/SystemTests/ display histograms from these ROOT files. Although these ROOT files reside in NFS, the access is (currently) fast enough.
>
> As our data serving needs grow, we may need to be smarter in how we configure and use xrootd, particularly with how we physically store our data. We are planning on acquiring a large number of NFS servers (large is a relative term here, which would probably translate into "tiny" in the context of BaBar) to store and serve our ROOT files from. As we learn about xrootd, maybe there are other alternatives we may want to consider.
>
> We are also considering using Richard Mount's tera-memory database to hold our reconstructed photon database entirely in memory for interactive data analysis. The idea was to serve this in-memory database using xrootd.
>
> We have much to learn, and I appreciate all of the timely and helpful emails I have received so far in helping us get started with xrootd.
>
> Warmest regards, Matt
>
>
> -----Original Message-----
> From: Andrew Hanushevsky [mailto:[log in to unmask]]
> Sent: Sunday, February 27, 2005 1:23 PM
> To: Gowdy, Stephen
> Cc: Langston, Matthew David; xrootd-l
> Subject: Re: How do we export multiple directories from xrootd.cf
>
> Hi Matt,
>
> Stephen is right. THe performance will not be very good. While you have
> eased the load on nfs in terms of number of clients the overall speed will
> be limited to below nfs speeds. In general, nfs is a very poor performer.
>
> Andy
>
> On Sun, 27 Feb 2005, Stephen J. Gowdy wrote:
>
> > Hi Matt,
> > 	BTW, do you really want to serve an NFS disk via xrootd? I'm not
> > sure what the benefits would be, perhaps teher server would cache the file
> > to make it a little better than normal NFS if a lot of people open the
> > same file...
> >
> > 							regards,
> >
> > 							Stephen.
> >
> > On Sun, 27 Feb 2005, Langston, Matthew David wrote:
> >
> > > We would like to export multiple directories from our xrootd server. The version of xrootd we are running currently only supports exporting one directory. This is our current xrootd.cf file:
> > >
> > > glast@glast01 $ cat xrootd.cf
> > > xrootd.fslib libXrdOfs.so
> > > oss.readonly
> > > xrootd.export /nfs/farm/g/glast/
> > >
> > > We would like to do something like this:
> > >
> > > glast@glast01 $ cat xrootd.cf
> > > xrootd.fslib libXrdOfs.so
> > > oss.readonly
> > > xrootd.export /nfs/farm/g/glast/dir1
> > > xrootd.export /nfs/farm/g/glast/dir2
> > >
> > > However, it appears that xrootd only takes the last "xrootd.export" stanza. Is there a way to get multiple exports (maybe in a later version of xrootd)?
> > >
> > > Warmest regards, Matt
> > >
> > >
> >
> > --
> >  /------------------------------------+-------------------------\
> > |Stephen J. Gowdy                     | SLAC, MailStop 34,       |
> > |http://www.slac.stanford.edu/~gowdy/ | 2575 Sand Hill Road,     |
> > |http://calendar.yahoo.com/gowdy      | Menlo Park CA 94025, USA |
> > |EMail: [log in to unmask]       | Tel: +1 650 926 3144     |
> >  \------------------------------------+-------------------------/
> >
>

--
 /------------------------------------+-------------------------\
|Stephen J. Gowdy                     | SLAC, MailStop 34,       |
|http://www.slac.stanford.edu/~gowdy/ | 2575 Sand Hill Road,     |
|http://calendar.yahoo.com/gowdy      | Menlo Park CA 94025, USA |
|EMail: [log in to unmask]       | Tel: +1 650 926 3144     |
 \------------------------------------+-------------------------/


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