Implement stage in/out

[ChristopherHogan]

Stage-in is bringing data from outside of Hermes into Hermes buffers, and stage-out is moving data from within Hermes to external storage. The can happen either as a separate job before/after the main application, or as part of the main application.

Before/after the job runs

This (I believe) is how typical HPC users define stage-in. The process would involve the following steps:

• Reserve nodes.
• Start a Hermes daemon (1 per node).
• Run a Hermes stage-in CLI tool.
• Run the main app as a client that attaches to the Hermes daemon.
• Run the Hermes stage-out CLI tool.
• Stop the daemon.

CLI parameters:

• list of files to stage in/out
• list of ranges for each file (future work. Initially we only work with entire files).
• DPE policy (if you want to override the default policy in hermes.conf).

Potentially need a CLI for each adapter.
Synchronous for now, but think about async for future versions.

As part of the job

In this version, the user supplies a list of files to stage-in as part of the config, then we will have triggers where data is loaded into Hermes from external sources. Anthony suggests using a different term for this process to distinguish it from the "stage-in" described above. Maybe "Load External Data".

Possible behavior:

• Load all external data on InitHermes. Synchronously or async.
• Load each external file when it's opened. Synchronously or async.
• Flush to external storage on file close.
• Flush to external storage on Hermes::Finalize.