What do "doesn't support DPO or FUA" and other disk cache messages mean ?
Issue
- When booting a system, the messages below about device caching are always output.
- When adding a disk to the system, the messages below are output during disk discovery.
- When plugging in a USB disk to the system, the messages below are output during discovery.
- Please explain what the following boot time messages mean:
sd 5:0:0:0: [sda] 209715200 512-byte logical blocks: (107 GB/100 GiB) sd 5:0:0:0: [sda] Write Protect is off sd 5:0:0:0: [sda] Mode Sense: 9f 00 00 00 sd 5:0:0:0: [sda] Write cache: disabled, read cache: disabled, doesn't support DPO or FUA sd 2:0:0:0: [sdb] 488281250 512-byte logical blocks: (250 GB/232 GiB) sd 2:0:0:0: [sdb] Write Protect is off sd 2:0:0:0: [sdb] Mode Sense: 00 3a 00 00 sd 2:0:0:0: [sdb] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA scsi9 : SCSI emulation for USB Mass Storage devices scsi 9:0:0:0: Direct-Access WDC WD32 00AAJS-00L7A0 PQ: 0 ANSI: 2 CCS sd 9:0:0:0: Attached scsi generic sg3 type 0 sd 9:0:0:0: [sdc] 625142448 512-byte logical blocks: (320 GB/298 GiB) sd 9:0:0:0: [sdc] Write Protect is off sd 9:0:0:0: [sdc] Assuming drive cache: write through scsi 1:0:0:0: Direct-Access DGC LUNZ 0532 PQ: 0 ANSI: 4 sd 1:0:0:0: [sdb] READ CAPACITY failed sd 1:0:0:0: [sdb] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE sd 1:0:0:0: [sdb] Sense Key : Illegal Request [current] sd 1:0:0:0: [sdb] Add. Sense: Logical unit not supported sd 1:0:0:0: Attached scsi generic sg2 type 0 sd 1:0:0:0: [sdb] Test WP failed, assume Write Enabled sd 1:0:0:0: [sdb] Asking for cache data failed sd 1:0:0:0: [sdb] Assuming drive cache: write through {virtual disk} sd 0:0:0:3: [sdd] 73400320 512-byte logical blocks: (37.5 GB/35.0 Gib) sd 0:0:0:3: [sdd] Write Protect is off sd 0:0:0:3: [sdd] Mode Sense: 61 00 00 00 sd 0:0:0:3: [sdd] Cache data unavailable sd 0:0:0:3: [sdd] Assuming drive cache: write through {on console during boot} Asking for cache data failed Assuming drive cache : write through
- Receiving message "doesn't support DPO or FUA", what does this mean?
- Why is disk write cache shown as disabled in "Write cache: enabled, read cache: enabled"?
- Receiving message "Assuming drive cache : write through", what does that mean?
- Do any of these messages mean there are problems with storage?
Environment
- Red Hat Enterprise Linux 6
- Red Hat Enterprise Linux 5
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