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ifdh cp locks

These are implemented via files in the Bluearc system,
using the same lock as the earlier 'cpn' scripts.

Details are documented under
https://cdcvs.fnal.gov/redmine/projects/ifdhcpn/wiki

Present characteristics

  • Locks are managed for each client group via files under /grid/data/<groupname>/LOCK
  • Locks can be handled at a net rate of about five per second.
  • Locks perform efficiently with queues of up to 50,000.

Open issues

Locks should be taken based on disks accessed, not the user's group.
Locks should be moved from /grid/data to /grid/app,
so that /grid/data can be moved to the data Bluearc head.
Locks could be done via a web service, for remote access and better latency.