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

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