h1fw0 had file write issues Friday afternoon. I power cycled the Solaris LDAS-QFS writer machine h1ldasgw0 and h1fw0 has been stable since then.
At the time h1ldasgw0 was rebooted it had been running since 14 Dec 2016 (163 days). For comparison, h1ldasgw1 has an uptime of 250 days. So we don't seem to be seeing a "running too long" issue and there is no explanation for h1ldasgw0's problem other than we have seen this before with the same solution.