amd64/127492: System hang on ZFS input-output

[Alex]

>Number:         127492
>Category:       amd64
>Synopsis:       System hang on ZFS input-output
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    freebsd-amd64
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Fri Sep 19 06:30:00 UTC 2008
>Closed-Date:
>Last-Modified:
>Originator:     Alex
>Release:        7.1
>Organization:
JSC "P.T.T."
>Environment:
FreeBSD x6.line1.ru 7.1-PRERELEASE FreeBSD 7.1-PRERELEASE #1: Mon Sep 15 11:27:50 MSD 2008     root at x6.line1.ru:/usr/obj/usr/src/sys/KMIST  amd64 
>Description:
We use RAID controller Smart Array P400 (driver ciss)in our system.
Five hardware stripe arrays was combined into raidz (zfs).

#df -h
coolpool         6.7T    1.7T    5.0T    25%    /www

/www - used by proftpd and httpd daemons
System is working properly during some period of time(day-week), but processes which are accessing to the ZFS volume turn into "D  uninterruptible wait" state and hang on.

www      86576  0.0  0.5 121560 19556  ??  D     7:37AM   0:00.00 /usr/local/sbin/httpd -DNOHTTPACCEPT
www      86577  0.0  0.5 121560 19556  ??  D     7:37AM   0:00.00 /usr/local/sbin/httpd -DNOHTTPACCEPT
www      86578  0.0  0.5 121560 19556  ??  D     7:38AM   0:00.00 /usr/local/sbin/httpd -DNOHTTPACCEPT

Any requests to the ZFS volume cause the process hang.
"Reboot"-command is executed normally up to the moment when the system produce "syncing disks" and hang also.

P.S. 7.0 - release is working in the same way.

>How-To-Repeat:
We don't know. Possible high disc load.
>Fix:
Hardware reset. O_o

>Release-Note:
>Audit-Trail:
>Unformatted: