Lightweight Replication of Heavyweight Data

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Lightweight Replication ofHeavyweight Data

• Scott Koranda
• University of Wisconsin-Milwaukee
• National Center for Supercomputing Applications

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Heavyweight Data from LIGO

• Sites at Livingston, LA (LLO) and Hanford, WA
  (LHO)
• 2 interferometers at LHO, 1 at LLO
• 1000s of channels recorded at rates of 16 KHz,
  16 Hz, 1 Hz,
• Output is binary frame files holding 16 seconds
  data with GPS timestamp
• 100 MB from LHO
• 50 MB from LLO
• 1 TB/day in total
• S1 run 2 weeks
• S2 run 8 weeks

4 km LIGO interferometer at Livingston, LA
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Networking to IFOs Limited

• LIGO IFOs remote, making bandwidth expensive
• Couple of T1 lines for email/administration only
• Ship tapes to Caltech (SAM-QFS)
• Reduced data sets (RDS) generated and stored on
  disk
• 20 size of raw data
• 200 GB/day

GridFedEx protocol
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Replication to University Sites
Cardiff
MIT
AEI
UWM
PSU
CIT
UTB
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Why Bulk Replication to University Sites?

• Each has compute resources (Linux clusters)
• Early plan was to provide one or two analysis
  centers
• Now everyone has a cluster
• Cheap storage is cheap
• 1/GB for drives
• TB RAID-5 lt 10K
• Throw more drives into your cluster
• Analysis applications read a lot of data
• Different ways to slice some problems, but most
  want access to large sets of data for a
  particular instance of search parameters

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LIGO Data Replication Challenge

• Replicate 200 GB/day of data to multiple sites
  securely, efficiently, robustly (no babysitting)
• Support a number of storage models at sites
• CIT ? SAM-QFS (tape) and large IDE farms
• UWM ? 600 partitions on 300 cluster nodes
• PSU ? multiple 1 TB RAID-5 servers
• AEI ? 150 partitions on 150 nodes with redundancy
• Coherent mechanism for data discovery by users
  and their codes
• Know what data we have, where it is, and
  replicate it fast and easy

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Prototyping Realizations

• Need to keep pipe full to achieve desired
  transfer rates
• Mindful of overhead of setting up connections
• Set up GridFTP connection with multiple channels,
  tuned TCP windows and I/O buffers and leave it
  open
• Sustained 10 MB/s between Caltech and UWM, peaks
  up to 21 MB/s
• Need cataloging that scales and performs
• Globus Replica Catalog (LDAP) lt 105 and not
  acceptable
• Need solution with relational database backend
  scales to 107 and fast updates/reads
• No need for reliable file transfer (RFT)
• Problem with any single transfer? Forget it, come
  back later
• Need robust mechanism for selecting collections
  of files
• Users/sites demand flexibility choosing what data
  to replicate
• Need to get network people interested
• Do your homework, then challenge them to make
  your data flow faster

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LIGO, err Lightweight Data Replicator (LDR)

• What data we have
• Globus Metadata Catalog Service (MCS)
• Where data is
• Globus Replica Location Service (RLS)
• Replicate it fast
• Globus GridFTP protocol
• What client to use? Right now we use our own
• Replicate it easy
• Logic we added
• Is there a better solution?

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Lightweight Data Replicator

• Replicated 20 TB to UWM thus far
• Just deployed at MIT, PSU, AEI
• Deployment in progress at Cardiff
• LDRdataFindServer running at UWM

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Lightweight Data Replicator

• Lightweight because we think it is the minimal
  collection of code needed to get the job done
• Logic coded in Python
• Use SWIG to wrap Globus RLS
• Use pyGlobus from LBL elsewhere
• Each site is any combination of publisher,
  provider, subscriber
• Publisher populates metadata catalog
• Provider populates location catalog (RLS)
• Subscriber replicates data using information
  provided by publishers and providers
• Take Condor approach with small, independent
  daemons that each do one thing
• LDRMaster, LDRMetadata, LDRSchedule, LDRTransfer,

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Future?

• LDR is a tool that works now for LIGO
• Still, we recognize a number of projects need
  bulk data replication
• There has to be common ground
• What middleware can be developed and shared?
• We are looking for opportunities
• Code for solve our problems for us
• Want to investigate Stork, DiskRouter, ?
• Do contact me if you do bulk data replication