Quantum 6-00360-15 manual Ungated files, Non-gated files

Figure 59 Sharing Access to Files

Appendix D Quality of Service Guide

Real-time I/O

This automatic clearing of real-time I/O is carried out in the context of the process that is closing the file. If the FSM cannot be reached for some reason, the request is enqueued on a daemon and the process closing the file is allowed to continue. In the background, the daemon attempts to inform the FSM that the real-time I/O has been released.

Different processes can share the same file in real-time and non-real-time mode. This is because the level of gating is at the handle level, not the file level. This allows a real-time process to perform ingest of material (video data) at the same time as non-real-time processes are performing other operations on the file.

In Figure 59, Process A has ungated access to file foo. Processes B and C also are accessing file foo, but the client gates their I/O accesses. If multiple handles are open to the same file and all are in real-time mode, only the last close of the handle releases the real-time I/O back to the system. This is because on most platforms the file system is informed only on the last close of a file.

	It is also possible to denote using the RT_NOGATE flag that a handle
Ungated files
	should not be gated without specifying any amount of real-time I/O. This
	is useful for infrequently accessed files (such as index files) that should
	not be counted against the non-real-time I/O. System designers typically
	allow for some amount of overage in their I/O subsystem to account for
	non-gated files.

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