topic Re: Path Switching in Operating System - OpenVMS

Path Switching

Kevin Raven (UK) — Mon, 09 Oct 2006 10:14:17 GMT

I have been testing path swithes between Top and Bottom fibre cards on a ES45 running OpenVMS 7.3-2 with Update V8 applied.
We have put together a simple srcipt to test the time it takes to switch path. The script simply loops creating files on a EMC SAN based disk. While the script runs we simply pull a fibre cable from one of the fibre cards on the server.
The path switch takes approx 5 seconds.
Can this be speeded up ?

Does a sysgen param exist to reduce the wait prior to path switch ?

Re: Path Switching

Robert Brooks_1 — Mon, 09 Oct 2006 10:45:34 GMT

No, the path switch cannot happen any quicker.

We have not done any testing with EMC storage, so I cannot say for sure how those controllers respond, our experience with HSZ, HSG, and HSV controllers show us that
there can be some amount of time (measured in seconds) before the controller will return an error back to the operating system.

The biggest consumer of time here is that we (multipath) need to wait for various SCSI commands to either "time out" or fail before we can move on to find a working path. When an I/O fails, multipath's algorithms are such that we try to stay on the current path, because we've found that the majority of problems are rather transient.

-- Rob, VMS Engineering

Re: Path Switching

Kevin Raven (UK) — Tue, 10 Oct 2006 04:42:17 GMT

Thanks for the quick reply.