SitesSetupAndConfiguration

Help and Support

  • The first entry point for sites is their cloud squad support: atlas-adc-cloud-XX at cern.ch .
  • In case of urgent matters please contact the ATLAS Computing Run Coordinator through atlas-adc-crc AT cern.ch .
  • For information that you believe is worth being discussed within the whole ATLAS distributed computing community use (don't abuse) atlas-project-adc-operations AT cern.ch .

Recommendations and mandatory services

Baseline middleware

Storage

  • Documentation on Grid storage deployment
  • Since 2019, SRMless storage is being implemented especially in DPM sites. More informations here
  • In order to keep the storages consistent with the Rucio catalogs, automatic consistency checks should run on regular basis. To do this, the sites are expected to provide storage dumps on a monthly or quarterly basis according the information here. Dumps are also expected in case a major incident affected the storage.

Computing Element

  • There are mainly 3 types of CEs, ARC-CE, CREAM-CE and now HTCondorCE
  • ARC-CE is now the one most commonly installed at new sites in Europe, HTCondorCE is typical in the US

Choice of Batch system

  • ATLAS would strongly recommend that the site run a batch system which works well with the CE it uses, allows job requirement passing, e.g. memory, cores, walltime and is integrated with cgroups. HTCondor and SLURM are very well supported in our experience.
  • ATLAS would prefer to have a fully dynamic configuration at site (possible with the above mentioned batch systems). The ATLAS payload scheduler, driven by the workflow management, will take care about optimizing the usage of the resources prioritizing the most mission critical jobs for ATLAS.
  • You can find a batch system comparison table with information also about LSF, torque-maui and UGE/SoGE here

Batch system shares and limits

  • As of February 2019 the target sharing of computing resources is recommended to be :
    • Tier2 : 25% analysis, 75% production
    • Tier1 : 5% analysis, 95% production
    • Analysis jobs come in burst so it can be that only few analysis jobs are assigned to the site
  • The type of jobs can be identified
    • Analysis jobs come with /atlas/Role=pilot while Production jobs with /atlas/Role=production
    • /atlas/Role=lcgadmin is used only for SAM tests which are very few jobs per hour (usually one) and they should have the highest priority and small fair share
  • Within production
    • If UCORE queues are installed , the share between Score and Mcore is managed dynamically by ATLAS. Only the Mcore queue will be used.
    • if UCORE is not yet installed by ATLAS, the share should be 80% multi-core (8 core) and 20% single core jobs with a dynamic setup.
  • cgroups: to control job resource usage as CPU/memory on kernel level, cgroups are a desirable feature. SLURM, HTCondor, LSF (>9.1), UGE (>8.2) all support cgroups at least to limit the memory.
  • ATLAS sites should really avoid killing ATLAS jobs based on VMEM info, VMEM does not represent physical memory used anymore, it indicates just the memory that can be mapped at some point, and in the 64bit era it can become a huge number compared to the memory actually used.
    • More about memory and how it is mapped to the different batch systems and CEs parameters can be found in the WLCG Multicore TF pages.
    • Batch systems like torque and SoGE are not integrated with cgroups and cannot handle limiting the memory correctly anymore. To protect sites from memory leaks even at these sites ATLAS jobs can now monitor the memory they use with a tool that extracts memory information from smaps and is working to make sure jobs are not exceeding the site specification using this information.

Worker Node hardware resources

A node should typically provide the following amount of hardware resources per single-core job slot

  • About 20 GB of disk scratch space, although 10-15 GB is workable.
    • For an 8 core MCORE slot, scratch space of 80-100GB is sufficient
  • At least 2 GB of (physical) RAM, but having 3-4 GB would be beneficial
  • Enough swap space such that RAM + swap >= 4 GB
  • As a rule of thumb, about 0.25 Gbit/s of network bandwidth (might want higher for more powerful CPUs).
  • CPU performance increases of up to ~40% (according to HEP-SPEC06) can be gained by using hyperthreading; in this case each node would require additional disk and RAM (and to a lesser extent, network bandwidth) to support the additional virtual cores.

Worker Node logical configuration

See AtlasWorkerNode : OBSOLETE

Squids

  • Sites are requested to have a squid (ideally two for resilience) to allow WN to access conditions data (Frontier) and CVMFS data (SW releases) in an efficient manner which won't put load on the ATLAS central services.
  • A Frontier Squid RPM, which works for both CVMFS and Frontier access, has been created which will setup a squid with suitable default settings, requiring only minimal configuration. See v2 or v3 instructions.
  • A standard Squid (3.x) can be configured to allow access to CVMFS, and may work for Frontier access (but there are potential issues for both v2 and v3 v2 and v3)
    • here are instructions for configuring a standard squid for CVMFS access
  • In either case follow the ATLAS-specific deployment instructions at AtlasComputing/T2SquidDeployment

Network

  • perfSONAR is also mandatory to understand and monitor Networks.
  • Each site should have two sets of perfSONAR services running: latency and bandwidth
  • It is possible since perfSONAR v3.4 to run both services on a single node which has at least two suitable NICs (network interface cards). See the link for details about deploying and configuring perfSONAR.

Recommended CPU, Storage and Network capacity

The latest basic recommendation for CPU and Storage and Network are available here in the agenda of the International Computing Board (for ATLAS users, will be attached to the twiki) https://indico.cern.ch/event/301690/, attached to this twiki for people without ICB indico access 20140227_ADCOpsSiteClassification_rev01.pdf

  • The numbers are just indications, they strongly depend on the sites and their configuration, obviously the WAN and LAN should be dimensioned depending on the number of cores.
  • DirectI/O (from WN to local storage) and remote data access also impact the networking infrastructure.
  • As order of magnitude: For a minimum Tier2 with 3k HEPSPEC06 and 200TB of disk space, the experience of Run1 tells us that we have about 200Mb/s sustained traffic
  • For LAN, we do have I/O hungry jobs which can require 40GB of inputs for an 8 core jobs and last 3/6hours, 10-20MB/s from/to WN - storage would be reasonable (check also above in the WN part the "rule of thumb" for the network bandwidth)

Limit concurrent FTS transfers to a destination (Optional)

The following lines can be used to limit the total number of concurrent transfers to a SE. Normally, input files are located in few places so only few concurrent FTS channels are used. But in case of dat rebalancing or PU distribution, the input files can be in > 50 sites which can be used by all FTS transfers. To protect storages with few disk servers, the number of parallel transfers can be limited with the following code. This should not be usefull by default.

from rucio.transfertool.fts3 import FTS3Transfertool


limits = {'srm://tech-se.hep.technion.ac.il': (150, 150)}

fts_hosts = ['https://lcgfts3.gridpp.rl.ac.uk:8446', 'https://fts3-pilot.cern.ch:8446', 'https://fts.usatlas.bnl.gov:8446', 'https://fts3-test.gridpp.rl.ac.uk:8446', 'https://fts3-atlas.cern.ch:8446', 'https://fts3-devel.cern.ch:8446']

for fts_host in fts_hosts:
    fts = FTS3Transfertool(fts_host)
    for se in limits:
        fts.set_se_config(se, inbound_max_active=limits[se][0], outbound_max_active=limits[se][1])
        #fts.set_se_config(se, staging=limits[se][0])

Configuration within ADC

  • The ATLAS Grid Information System (AGIS) is the service where the ATLAS site services and the ATLAS topology are described.
  • Once your site has been setup you need to get in contact with your cloud squad (atlas-adc-cloud-XX at cern.ch ) to make sure that your site, the DDM endpoint (AKA RucioStorageElement RSE), and the PandaResources(AKA PandaQueue) are properly defined in AGIS.
  • As noted in the perfSONAR instructions you also need to register your perfSONAR installation in either GOCDB or OIM (for OSG sites).

Documentation of deployment steps

Follow this procedure

Documentation on operation

Global overview WLCG

Global overview ATLAS

Site availability reliability

Site blacklisting

Site status can be found in ATLAS Sam monitoring or AGIS

Typical ATLAS jobs

In this twiki ATLASJobs we are trying to summarize some of the typical ATLAS jobs in terms of memory requirements, I/O, etc

Grid Storage

Grid site decomissioning

In order to minimise the impact on ATLAS users and production, the site decomissioning should be organised well in advance and coordinated with ADC

The decomissioning follow up should be done through a JIRA ticket in ADCINFR project (squad/site responsible). The responsibilities between Central Operation and site/squad are detailed.

The CPU could be used untill the last moment by accessing data still on SE or remote SE. In contrary, the decommissioning of the storage part should be organised well in advance (up to 3 months) to replicate data somewhere else (if necessary) and clean properly Rucio catalog : it avoids to still host data when the deadline is reached. The main bottleneck for this procedure is the discovery and proper cleaning of lost files.

  • Updating Panda queues
    • if the CPU usage should be stopped : site admin declares downtime in GOCB/OIM the services associated to the PQ (CE, squid). A quicker procedure is to ask cloud squad or ADC Central to set OFFLINE in AGIS and then flag it as disable.
    • if the CPU usage should continue cloud squad or ADC Central should update the PQ :
      • to write output in new SE (Update the read_wan)
      • to add, when necessary, a read_lan to access remote SE
      • to remove, when necessary, the read_lan to local SE
  • For the Grid storage part, follow this procedure
  • When previous steps done, stop all other services in AGIS (* squad responsible or ADC central*)

Site already broken

One needs to understand the status in AGIS and their impact on ADC tools (rules seem different for US sites):

  • 'Certification Status' for an AGIS site ('uncertified' or 'suspended' or 'closed')
  • 'Status' which can be 'active', 'production', none
  • 'STATE' : How can a site be ACTIVE and bad for 'Certification Status' or 'Status'

Grid component decomissioning or migration

To stop the usage of a Grid component (CE, SE , Panda queue, DDM endpoint)

  • a JIRA ticket in ADCINFR project should be issued to follow up
  • a downtime of the service should be declared in GOCDB/OIM
  • AGIS has to be updated accordingly (squad or site responsibility) This is done by the local squad or ADC central (first this last case, post a JIRA ticket in ADCINFR project).

WLCG site : Replacing a SE with another SEs

WLCG site : migration to diskless sites

Small WLCG sites are recommanded to focus investments in CPUs instead of storage to optimise the ADC support and site manpower. This does not prevent to keep LOCALGROUPDISK endpoint. To contribute to production, such sites should be setup to run local CPUs and access input files from a remote site and write output to the remote site ('diskless sites'). The technical requirements to pair a diskless site to a remote SE :

  • A network connectivity big enough
  • A remote SE able to sustain the additional load.

This setup is similar to cloud sites. Another option is to setup an ARC-CE to benefit from its caching mechanism. On 1st January 2017, the UNI-DORTMUND and SIEGEN sites follow this configuration.

To transform small sites with existing SE to diskless ones, the following procedure should be followed :

  • The decision to migrate a WLCG site to diskless is taken by the cloud coordination and the country ICB representative. They should also define the remote SE (usually the biggest one in the country). These informations are transfered to ADC coordination to trigger the migration. To initiate this migration in 2017, the ICB-ADC responsible has contacted ICB representatives to recommand this migration.
  • ADC coordination initiates a JIRA ticket in ADCINFRA, with site representative and associated squad in CC to :
    • Request somebody at the diskless site to check on a WN that it can read/write a file on the remote Storage Element using protocole at destination (should fail only in case of port not opened outside)
      • Testing read : lsetup rucio ; Setup proxy for ATLAS ; rucio download --rse ENDPOINT --nrandom 1 DATASET (DATASET=hc_test.pft or hc_test.aft )
      • Testing write : * Can only be done with Production Role to write on DATADISK* ; rucio upload ...
    • Transform Panda queues to use remote SE (more details) . ATLAS SAM tests on local SE will stopped automatically. This new configuration is tested over few weeks to validate that the remote SE can sustain this additional load. Untill this point it is easy to switch to the local SE again
    • After the validation period, DDM Ops and cloud squad will make the necessary steps to decommission the SE : Procedure
      • Cleaning LOCALGROUPDISK endpoints : Organised by cloud squad (deletion by replica owner or with atlas//Role=production)
      • Remove the SE description from AGIS (cloud squad)

When the migration on the ATLAS side is finished, the site admin proceeds with the decomissioning in WLCG/OIM. The recommended steps are :

  • It should update the GOCDB to declare the SE no more in production. Then Ops SAM tests will be stopped automatically
  • The SE can be physically decomissioned.

Opportunistic Resources

In this twiki OpportunisticResources

Blacklisting of permanently broken site

In the ICB meeting on 12th December 2017, the Funding Agency reps have agreed to endorse the following policy for permanently broken sites :

  • Broken site over > 1 month with no concreate action although informed through GGUS -> site permanently blacklisted in AGIS (site informed through the pending GGUS ticket which can be closed)
  • Each year, permanently blacklisted sites are reviewed and most probably completly decommissioned in AGIS and Rucio (ICB rep + AGIS site contact informed)

Added after ICB :

  • If the issue concerns SE, the site PQ can be changed to point to another SE but it requires the agreement of the destination site

FAQ

Frequently asked questions by sites


Major updates:
-- AleDiGGi - 2015-09-16

Responsible: AleDiGGi
Last reviewed by: Never reviewed

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf 20140227_ADCOpsSiteClassification_rev01.pdf r1 manage 512.3 K 2016-01-07 - 15:50 AleDiGGi  
PDFpdf DISKLESS_MEMO_EV_.pdf r1 manage 210.0 K 2017-05-21 - 16:51 StephaneJezequel Procedure set Panda queue to access remote SE
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Topic revision: r54 - 2019-09-19 - StephaneJezequel
 
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