Hi
I little bit more information: 
The disk /dev/disk/dsk9c is in a SAN (StorageWorks - HSG80)
In /var/adm/messages I found the following messages:
Nov 14 14:00:06 vmunix: drd_handle_eei: Device 177. errno 5Uninterpreted
b_eei value 0x100.
Nov 14 14:00:06 vmunix: AdvFS I/O error:
Nov 14 14:00:06 vmunix:     Volume: /dev/disk/dsk9c
Nov 14 14:00:06 vmunix:     Tag: 0xfffffff0.0000
Nov 14 14:00:06 vmunix:     Page: 3265
Nov 14 14:00:06 vmunix:     Block: 17628976
Nov 14 14:00:06 vmunix:     Block count: 16
Nov 14 14:00:06 vmunix:     Type of operation: Write
Nov 14 14:00:06 vmunix:     Error: 5
Nov 14 14:00:06 vmunix:     EEI: 0x100
Nov 14 14:00:06 vmunix:
Nov 14 14:00:06 vmunix: bs_osf_complete: metadata write failed
Nov 14 14:00:06 vmunix: AdvFS Domain Panic; Domain data_domain Id
0x3cb1981d.010c2299
Nov 14 14:00:06 vmunix: An AdvFS domain panic has occurred due to either a
metadata write error or an internal
 inconsistency. This domain is being rendered inaccessible.
Nov 14 14:00:06 vmunix: AdvFS I/O error:
Nov 14 14:00:06 vmunix:     A read failure occurred - the AdvFS domain is
inaccessible (paniced)
Nov 14 14:00:06 vmunix:     Volume: /dev/disk/dsk9c
Nov 14 14:00:06 vmunix:     Tag: 0xfffffff0.0000
Nov 14 14:00:06 vmunix:     Page: 122
Nov 14 14:00:06 vmunix:     Block: 17580736
Nov 14 14:00:06 vmunix:     Block count: 16
Nov 14 14:00:06 vmunix:     Type of operation: Read
Nov 14 14:00:06 vmunix:     Error: 5
Nov 14 14:00:06 vmunix:     EEI: 0x300
Thanks.
Best regards,
Stephane
-----Ursprungliche Nachricht-----
Von: Moser Stephane RUAG M 
Gesendet: Thursday, November 14, 2002 3:18 PM
An: 'tru64-unix-managers_at_ornl.gov'
Betreff: WG: EVM ALERT [600]: AdvFS: An AdvFS domain panic has occurred
on data_domain
Hi everybody
On my TruCluster v51a (Patch Kit 1) I had an AdvFS domain panic (see below).
Any idea ... patches ?
In advance Thanks
Best regards,
Stephane
============================ EVM Log event ===========================
EVM event name: sys.unix.fs.advfs.fdmn.panic
    This event is posted by the AdvFS filesystem to indicate that an
    AdvFS domain panic has occurred on the specified domain.  This is
    due to either a metadata write error or an internal inconsistency.
    The domain is being rendered inaccessible.
    Action: Please refer to the guidelines in the AdvFS Guide to File
    System Administration for the steps to recover this domain.
======================================================================
Formatted Message:
    AdvFS: An AdvFS domain panic has occurred on data_domain
Event Data Items:
    Event Name        : sys.unix.fs.advfs.fdmn.panic
    Cluster Event     : True
    Priority          : 600
    PID               : 524288
    PPID              : 0
    Event Id          : 139174
    Member Id         : 1
    Timestamp         : 14-Nov-2002 14:00:06
    Host IP address   : <IP>
    Cluster IP address: <IP>
    Host Name         : <Name>
    Cluster Name      : <Name>
    Format            : AdvFS: An AdvFS domain panic has occurred on $domain
    Reference         : cat:evmexp.cat:450
Variable Items:
    domain (STRING) = "data_domain"
======================================================================
Received on Thu Nov 14 2002 - 14:47:08 NZDT