[SunHELP] scsi

Hi, I have a trouble with the internal disk of a sparc Ultra 2 solaris 2.6,
openboot 3.7m  after booting the server, it's all right for quite a moment
and after that it goes down again, sends "I/O error" after performing any
command, the last of the /var/adm/messages says this:

Sep  5 17:26:27 pelimnoc2sua1 unix: WARNING:
/sbus at 1f,0/SUNW,fas at e,8800000/sd at 1,0 (sd1):
Sep  5 17:26:27 pelimnoc2sua1 unix:     SCSI transport failed: reason
'incomplete': retrying command
Sep  5 17:26:30 pelimnoc2sua1 unix: WARNING:
/sbus at 1f,0/SUNW,fas at e,8800000/sd at 1,0 (sd1):
Sep  5 17:26:30 pelimnoc2sua1 unix:     disk not responding to selection
Sep  5 17:30:47 pelimnoc2sua1 unix: fas:        1.0: cdb=[ 0x28 0x0 0x0 0x8c
0xfd 0x6d 0x0 0x0 0x2 0x0 ]
Sep  5 17:30:47 pelimnoc2sua1 unix: WARNING: /sbus at 1f,0/SUNW,fas at e,8800000
(fas0):
Sep  5 17:30:47 pelimnoc2sua1 unix:     Disconnected tagged cmd(s) (1)
timeout for Target 1.0
Sep  5 17:30:47 pelimnoc2sua1 unix: WARNING:
/sbus at 1f,0/SUNW,fas at e,8800000/sd at 1,0 (sd1):
Sep  5 17:30:47 pelimnoc2sua1 unix:     SCSI transport failed: reason
'timeout': retrying command
Sep  5 17:30:47 pelimnoc2sua1 unix: WARNING:
/sbus at 1f,0/SUNW,fas at e,8800000/sd at 1,0 (sd1):
Sep  5 17:30:47 pelimnoc2sua1 unix:     SCSI transport failed: reason
'reset': retrying command
Sep  5 17:30:50 pelimnoc2sua1 unix: WARNING:
/sbus at 1f,0/SUNW,fas at e,8800000/sd at 1,0 (sd1):
Sep  5 17:30:50 pelimnoc2sua1 unix:     SCSI transport failed: reason
'incomplete': retrying command

any help please!
thanks a lot
Mery