各位大大帮看下：datafile经常脱机需要media recovery什么原因？

服务器环境：win server 2000+oracle817i
有一datafile:size 8500M,最近经常脱机，找了很多原因，查了很多资料，没能找到原因，
各位高人，路过请指点一二。。。。。。。
alert.log:
Wed Oct 29 03:02:59 2008
ARCH shutting down
ARC0: Archival stopped
Starting up ORACLE RDBMS Version: 8.1.7.0.0.
System parameters with non-default values:
  processes                = 500
  timed_statistics         = TRUE
  shared_pool_size         = 406764540
  large_pool_size          = 614400
  java_pool_size           = 32768
  control_files            = d:\orant\database\control01.ctl, d:\orant\database\control02.ctl, d:\orant\database\control03.ctl
  db_block_buffers         = 29792
  db_block_size            = 4096
  compatible               = 8.1.0
  log_archive_start        = TRUE
  log_archive_dest_1       = location=e:\archive
  log_archive_format       = %%ORACLE_SID%%T%TS%S.ARC
  log_buffer               = 32768
  log_checkpoint_interval  = 10000
  log_checkpoint_timeout   = 1800
  db_files                 = 1024
  db_file_multiblock_read_count= 8
  max_enabled_roles        = 120
  remote_login_passwordfile= NONE
  global_names             = TRUE
  distributed_transactions = 10
  instance_name            = orcl
  service_names            = orcl
  sort_area_size           = 65536
  sort_area_retained_size  = 65536
  db_name                  = orcl
  open_cursors             = 300
  os_authent_prefix        =
  job_queue_processes      = 6
  parallel_max_servers     = 5
  background_dump_dest     = c:\oracle\admin\orcl\bdump
  user_dump_dest           = c:\oracle\admin\orcl\udump
  max_dump_file_size       = 10240
  oracle_trace_collection_name=
PMON started with pid=2
DBW0 started with pid=3
LGWR started with pid=4
CKPT started with pid=5
SMON started with pid=6
RECO started with pid=7
SNP0 started with pid=8
SNP1 started with pid=9
SNP2 started with pid=10
SNP3 started with pid=11
SNP4 started with pid=12
SNP5 started with pid=13
Wed Oct 29 03:03:16 2008
ARCH: STARTING ARCH PROCESSES
ARC0 started with pid=14
Wed Oct 29 03:03:16 2008
ARCH: STARTING ARCH PROCESSES COMPLETE
Wed Oct 29 03:03:16 2008
alter database  mount
Wed Oct 29 03:03:17 2008
ARC0: Archival started
Wed Oct 29 03:03:22 2008
Successful mount of redo thread 1, with mount id 1197101306.
Wed Oct 29 03:03:22 2008
Database mounted in Exclusive Mode.
Completed: alter database  mount
Wed Oct 29 03:03:22 2008
alter database open
Wed Oct 29 03:03:25 2008
Errors in file c:\oracle\admin\orcl\bdump\orclLGWR.TRC:
ORA-01110: data file 29: 'D:\ORANT\DATABASE\APINPBILL.DBF'
ORA-01114: IO error writing block to file 29 (block # 1)
ORA-27072: skgfdisp: I/O error
OSD-04008: WriteFile() failure, unable to write to file
O/S-Error: (OS 5) 拒绝访问。

Wed Oct 29 03:03:25 2008
Thread 1 opened at log sequence 283338
  Current log# 2 seq# 283338 mem# 0: D:\ORANT\DATABASE\REDO02.LOG
Successful open of redo thread 1.
Wed Oct 29 03:03:25 2008
SMON: enabling cache recovery
SMON: enabling tx recovery
Wed Oct 29 03:03:35 2008
Completed: alter database open
Wed Oct 29 03:16:25 2008
Thread 1 advanced to log sequence 283339
Wed Oct 29 03:16:25 2008
ARC0: Beginning to archive log# 2 seq# 283338
Wed Oct 29 03:16:25 2008
  Current log# 3 seq# 283339 mem# 0: D:\ORANT\DATABASE\REDO03.LOG
Wed Oct 29 03:16:25 2008
kcrrga: Warning.  Log sequence in archive filename wrapped
to fix length as indicated by %S in LOG_ARCHIVE_FORMAT.
Old log archive with same name might be overwritten.
ARC0: Completed archiving log# 2 seq# 283338
Wed Oct 29 03:34:55 2008
KCF: write/open error block=0x1f95ba online=1
     file=29 D:\ORANT\DATABASE\APINPBILL.DBF
     error=27072 txt: 'OSD-04008: WriteFile() failure, unable to write to file
O/S-Error: (OS 5) 拒绝访问。'
Automatic datafile offline due to write error on
file 29: D:\ORANT\DATABASE\APINPBILL.DBF
KCF: write/open error block=0x1fa2f9 online=0
     file=29 D:\ORANT\DATABASE\APINPBILL.DBF
     error=27072 txt: 'OSD-04008: WriteFile() failure, unable to write to file
O/S-Error: (OS 5) 拒绝访问。'
KCF: write/open error block=0x1fa8ca online=0
     file=29 D:\ORANT\DATABASE\APINPBILL.DBF
     error=27072 txt: 'OSD-04008: WriteFile() failure, unable to write to file
O/S-Error: (OS 5) 拒绝访问。'
KCF: write/open error block=0x691f3 online=0
     file=29 D:\ORANT\DATABASE\APINPBILL.DBF
     error=27072 txt: 'OSD-04008: WriteFile() failure, unable to write to file
O/S-Error: (OS 5) 拒绝访问。'
KCF: write/open error block=0x1f95bb online=0
     file=29 D:\ORANT\DATABASE\APINPBILL.DBF
     error=27072 txt: 'OSD-04008: WriteFile() failure, unable to write to file
O/S-Error: (OS 5) 拒绝访问。'
KCF: write/open error block=0x1219a6 online=0
     file=29 D:\ORANT\DATABASE\APINPBILL.DBF
     error=27072 txt: 'OSD-04008: WriteFile() failure, unable to write to file
O/S-Error: (OS 5) 拒绝访问。'
KCF: write/open error block=0x1fa8cb online=0
     file=29 D:\ORANT\DATABASE\APINPBILL.DBF
     error=27072 txt: 'OSD-04008: WriteFile() failure, unable to write to file
O/S-Error: (OS 5) 拒绝访问。'
KCF: write/open error block=0x122437 online=0
     file=29 D:\ORANT\DATABASE\APINPBILL.DBF
     error=27072 txt: 'OSD-04008: WriteFile() failure, unable to write to file
O/S-Error: (OS 5) 拒绝访问。'
KCF: write/open error block=0x1f8e6d online=0
     file=29 D:\ORANT\DATABASE\APINPBILL.DBF
     error=27072 txt: 'OSD-04008: WriteFile() failure, unable to write to file
O/S-Error: (OS 5) 拒绝访问。'
Wed Oct 29 06:51:45 2008
Thread 1 advanced to log sequence 283340
Wed Oct 29 06:51:45 2008
  Current log# 1 seq# 283340 mem# 0: D:\ORANT\DATABASE\REDO01.LOG
Wed Oct 29 06:51:46 2008
ARC0: Beginning to archive log# 3 seq# 283339
Wed Oct 29 06:51:46 2008
kcrrga: Warning.  Log sequence in archive filename wrapped
to fix length as indicated by %S in LOG_ARCHIVE_FORMAT.
Old log archive with same name might be overwritten.
ARC0: Completed archiving log# 3 seq# 283339
Wed Oct 29 07:39:43 2008