Page History

• xrootd
  • requires Requires more bookkeeping because it has no "ls".
  • I don't trust it - I'm aware that it's not intended to be a drop-in replacement for a disk-based filesystem, and I'm still trying to understand and internalize how it differs from one.
  • Could stage input or output files in parallel.
• Combine steps
  • reduces Reduces ability to roll back errors.
  • increases Increases latency.
• Varying crumb size
  • makes Makes lots of small crumbs, so digi files get read many times.
• Varying chunk size
  • lots Lots of small chunks mean more jobs are reading in parallel at the start of processing, but it does not increase the amount of data that's read.
  • If there are more chunks than available cores, that automatically throttles I/O somewhat.

• Use scratch disks
  • need Need to be able to leave files on scratch for a couple of hours without having a process running.
  • need Need to be able to copy files between batch machines with a process only at the receive end of the transfer.
  • Scalable scalable
    • But, maybe, it doesn't have to scale, it just has to work.  It's not like we're going to get mentioned on slashdot and suddenly have100x the data flowing in.

• Not stage files stored on AFS to/from scratch
  • AFS' internal caching means that we are copying the data twice.
  • This may be particularly useful for recon, where crumb jobs don't use the whole input file.

• PROOF
  • seems Seems deeply tied to xroot - needs xrootd to run on the batch host? 

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