Currently:

Three 'File Marks' per file are written now by Castor (with a small data packet before and after the file), to help identifying tape positions. This is historical since ~15-20 years. File marks take 3 seconds on the LTO drive and more on the IBM drives, limiting effective bandwidth depending on file size. After each file (and command to write a filemark), Castor flushes the tape drive buffer which can be as large as 128MB. When this is done, the file is 'commited' (marked as written to tape) and the next file is accepted for writing.

Proposed changes:

• enforce BIG files (~10GB) by stager policy, eg. simply don't accept smaller ones. Probably politically very incorrect.
• see whether we can live without filemarks or lower the frequency they are needed with, eg. by using an internal structure in ArchiveFiles we write instead of directly writing user files. See TestContinuousStream.
• we could probably avoid flushing that drive buffer - but when do we 'commit' the file then?
• we could write but one filemark

-- AndrasHorvath - 25 Apr 2005

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