“Managing a farm without user jobs would be easier” Clusters and Users at CERN Tim Smith...

“Managing a farmwithout user jobswould be easier”

Clusters and Users at CERN

Tim Smith CERN/IT

2002/10/25 HEPiX fall 2002: [email protected] 2

Contents

The road to shared clusters Batch cluster

Configuration User challenges Addressing the challenges

Interactive cluster Load balancing

Conclusions


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Solaris

The Demise of Free Choice

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Cluster Aggregation

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lxbatch

testbedtomog

tapes

pcsf

nomad

na49

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mta

l3c

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ccf

atlas

alice


Organisational Compromises

Clusters per Groups Sized for the average

users

Sized for user peaks users financiers : wasted resources

Invest effort in recooperating cycles for other groups

Configuration differences / specialities

Bulk Production Clusters Production fluctuations dwarf those in user

anal Complex cross-submission links


Production Farm: Planning

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ATLAS on

ALICE on

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LCG limit


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DNS load balancing

LSF

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750 Batch Servers

70 InteractiveServers

120 Disk Servers


Simple, Uniform

Shared Cluster ?


Partitioning

Still have identified resources Uniform configuration

Sharing Repartitioning or soak-up queues

If owner experiment reclaims resources, must suspend soak-up jobs – stranded jobs

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LSF Fair-Share

Trade-in partition for a share Multilevel

ATLAS 10%, CMS 12%, … cmsprod 45%, HiggsWG 15%, … usera 10%, userb 80%, userc 10%

Extra shares for productions Effort: Juggling resources to Accounting

Demonstrating fairness Protecting Policing


Facts and Figures

Accounting LSF job records Process with C-program Load into Oracle DB Prepare plots/tables with Crystal

Reports package LSFAnalyser ?

Monitoring Poll the user access tools SiteAssure ?


CPU Time / WeekMerged user analysisand production farms


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# pending % free # not placed # users

Performance of BatchJob Slot Analysis

Thu Fri Sa

10 min / tick


Challenging Batch (I)

Probing boundaries Flooding Concurrent starts Uncontrolled status polling

Hitting limits Disk space /tmp /pool /var Memory, Swap Full

Guarantees for other user jobs?

System Issues Queue drainers


Challenging Batch (II)

Un-Fair-Share Logging onto batch machines Batch jobs which resubmit themselves Forking sessions back to remote hosts

Wasting resources Spawning processes which outlive the jobs Sleeping processes Copying large AFS trees Establishing connections to dead machines


Counter Measures

File system quotas Virtual memory limits Concurrent jobs limits per

user/group Restricted access through PAM Instant response queues Master node setup

Dedicated, 1GB memory Failover cluster


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DNS load balancing

LSF

disk001

rfio

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750 Batch Servers


120 Disk Servers

LSFMultiCluster


Shared Clusterslx

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DNS load balancing

LSF

disk001

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750 Batch Servers


120 Disk Servers

SingleCluster


Interactive Cluster

DNS load balancing (ISS) Weighted load indexes

load, memory swap rate, disk IO rate # processes, # sessions, # window mgr

sessions

Exclusion thresholds file systems full, nologins

DNS publish 2 every 30 seconds Random from lowest 5


Daily Users

35 users/ node


Challenging Interactive

Sidestep load balancing

Parallel sessions across farm

Running daemons Brutal logouts

Open connections Defunct processes CPU sapping orphaned

processes

Monitoring+

beniced+

Monthly reboots


Interactive Reboots


Conclusions

Shared clusters present more user opportunities Both Good and Bad !

Don’t represent a panacea for sysadmins !

“Managing a farm without user jobs would be easier” Clusters and Users at CERN Tim Smith...

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