Oracle home headscratcher

We've got multiple Oracle homes on a Solaris 11.4 server (T8 SPARC). We are having issues with a single home (12.2.0.1), while others are fine (19.5, a different 12.2.0.1 home). We haven't seen this problem on any other hosts, and no known modifications to the environment happened prior to the behavior we're seeing.

Sqlplus appears to hang, but does eventually connect (by eventually, I'm talking 10+ minutes, and a local connection). This behavior extends to tnsping (times out, we traced but didn't get much), but running opatch for example, is not affected. Standby database on the system fall behind. External connections to databases are not impacted; only attempting to run the binaries locally from the problematic home exhibit the symptoms.

Our only clue on the host is very high utilization of our /u01 mount point, but so far our Unix crew hasn't been able to isolate which process is driving the IO.

Yesterday, on a whim we switched the problematic Oracle home permissions to 755 (from 700), and things "magically" worked and IO plummeted instantly.

Today, we switched back to 700 to see if we could break thing again; we did. However in this second case, chmod'ing the problematic home back to 755 had zero effect and the hanging behavior persists.

Any thoughts on what to look at next? Again, the problem is isolated to just this single home.

Thanks- Chris

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