Virtual MSSThe first steps
Some new directionsAbout the new ALICE::CERN::SE
Fabrizio FuranoCERN IT/GS
22-July-08ALICE TF Meeting
http://savannah.cern.ch/projects/xrootdhttp://xrootd.slac.stanford.edu
Fabrizio Furano - The Scalla suite and the Xrootd 2
Basic Scalla/XRootD working principle
July-2008
cmsdxrootd
cmsdxrootd
cmsdxrootd
cmsdxrootd
Client
A small2-level cluster.
Can hold
Up to 64 servers
Simple LAN clusters
July-2008Fabrizio Furano - The Scalla suite and the Xrootd 3
cmsdxrootd
cmsdxrootd
cmsdxrootd
cmsdxrootd
Simple clusterUp to 64 data servers1-2 mgr redirectors
cmsd
cmsdxrootd
cmsdxrootd
cmsdxrootd
cmsdxrootd
cmsdxrootd cmsd
xrootdcmsd
xrootd
cmsdxrootd
cmsdxrootd cmsd
xrootdcmsd
xrootd
cmsdxrootd
cmsdxrootd
Advanced clusterUp to 4096 (2 lvls) or
262K (3 lvls) data servers
Everything can have hot spares
Fabrizio Furano - The Scalla suite and the Xrootd 4
Purpose:◦A request for a missing file comes at cluster X,
◦X assumes that the file ought to be thereAnd tries to get it from the collaborating clusters, from the fastest one
Note that X itself is part of the game◦And it’s composed by many servers
The idea is that◦Each cluster considers the set of ALL the others like a
very big online MSS
◦This is much easier than what it seemsSlowly Into production for ALICE
Virtual MSS
July-2008
Cluster Globalization… an example
July-2008Fabrizio Furano - The Scalla suite and the Xrootd 5
cmsd
xrootdPragueNIHAM
… any other
cmsd
xrootd
CERN
cmsd
xrootd
ALICE global redirector (alirdr)all.role meta managerall.manager meta alirdr.cern.ch:1312
root://alirdr.cern.ch/Includes
CERN, GSI, and othersxroot clusters
Meta Managers can be geographically
replicatedCan have several in different places for region-aware load
balancing
cmsd
xrootd
GSIall.manager meta alirdr.cern.ch:1312 all.manager meta alirdr.cern.ch:1312 all.manager meta alirdr.cern.ch:1312all.role manager all.role manager all.role manager
Fabrizio Furano - The Scalla suite and the Xrootd 6
Up to now, xrootd clusters could be populated◦With xrdcp from an external machine
◦Writing to the backend store (e.g. CASTOR/DPM/HPSS etc.) E.g. FTD in ALICE now uses the first. It “works”…
Load and resources problemsAll the external traffic of the site goes through one machine
Close to the dest cluster
If a file is missing or lost◦For disk and/or catalog screwup
◦Job failure... manual intervention neededWith 107 online files finding the source of a trouble can be
VERY tricky
Cluster globalization
July-2008
Global redirector acts as a WAN xrootd meta-managerLocal clusters subscribe to it◦And declare the path prefixes they export
◦Local clusters (without local MSS) treat the globality as a very big MSS
◦Coordinated by the Global redirectorLoad balancing, negligible loadPriority to files which are online somewherePriority to fast, least-loaded sitesFast file location
True, robust, realtime collaboration between storage elements!
◦Very attractive for tier-2s
Many pieces
July-2008Fabrizio Furano - The Scalla suite and the Xrootd 7
cmsd
xrootd
GSI
The Virtual MSS Realized
July-2008Fabrizio Furano - The Scalla suite and the Xrootd 8
cmsd
xrootd PragueNIHAM
… any other
cmsd
xrootd
CERN
cmsd
xrootd
ALICE global redirector
all.role meta managerall.manager meta alirdr.cern.ch:1312
all.role manager all.role managerall.role manager
Note:the security hats could require
you use xrootdnative proxy support
But missing a file?Ask to the global metamgr
Get it from any othercollaborating cluster
all.manager meta alirdr.cern.ch:1312 all.manager meta alirdr.cern.ch:1312 all.manager meta alirdr.cern.ch:1312
Local clients worknormally
A particular way to use the same pieces of the vMSS
In order to phase out an old SE◦Keeping its content!
Advantages◦Files are spread evenly load balancing is effective
◦More used files are fetched typically firstDefault vMSS config will be restored soon◦Fetch from the global rdr
But it’s already subscribed to the global rdr
The ALICE::CERN::SE July trick
July-2008Fabrizio Furano - The Scalla suite and the Xrootd 9
cmsd
xrootd
New SE(starting empty)
The ALICE::CERN::SE July trick
July-2008Fabrizio Furano - The Scalla suite and the Xrootd 10
cmsd
xrootd
Old CERN::ALICE::SE(full)
cmsd
xrootd
ALICE global redirector
LOADGridShuttleother
The mechanism is there, fully “boxed”◦The new setup does almost everything it’s needed
A (good) side effect:◦Pointing an app to the “area” global redirector gives complete,
load-balanced, low latency view of all the subscribed SEs
◦An app using the “smart” WAN mode can just runProbably now a full scale production/analysis won’t
But what about an interactive small analysis on a laptop?
After all, HEP sometimes just copies everything, useful and not
I cannot say that in some years we will not have a more powerful WAN infrastructure
And using it to copy more useless data looks just ugly
If a web browser can do it, why not a HEP app? Looks just a little more difficult.
Better if used with a clear design in mind
Virtual MSS
July-2008Fabrizio Furano - The Scalla suite and the Xrootd 11
XrdCASTOR subscription to the Global redirector◦Needs a complete xrd refurbishment, very old versions
The new xrootd packages will be published shortly◦1-2 weeks. Just some minor fixes, to avoid troubles
◦Verify that the ML info is there (should be)Migration of the tier-2s?◦They have very old versions too
◦This should be quite easy for pure-xrootd sitesXrd-DPM refurbishment?◦With consequent subscription to the global rdr
◦Needs a complete xrd refurbishment, very old versions3rd party fetches development◦Reduce load on FTD
◦Put the DCaches into the vMSS game in some way
What’s missing
July-2008Fabrizio Furano - The Scalla suite and the Xrootd 12
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