I have a DELL server with PERC H700 Integrated controller. I've made RAID5 with 12 harddrives and the virtual device is in Optimal state, but I receive such errors under linux: sd 0:2:0:0: [sda] Unhandled error code sd 0:2:0:0: [sda] Result: hostbyte=0x07 driverbyte=0x00 sd 0:2:0:0: [sda] CDB: cdb[0]=0x88: 88 00 00 00 00 07 22 50 bd 98 00 00 00 08 00 00 end_request: I/O error, dev sda, sector 30640487832 sd 0:2:0:0: [sda] Unhandled error code sd 0:2:0:0: [sda] Result: hostbyte=0x07 driverbyte=0x00 sd 0:2:0:0: [sda] CDB: cdb[0]=0x88: 88 00 00 00 00 07 22 50 bd 98 00 00 00 08 00 00 end_request: I/O error, dev sda, sector 30640487832 sd 0:2:0:0: [sda] Unhandled error code sd 0:2:0:0: [sda] Result: hostbyte=0x07 driverbyte=0x00 sd 0:2:0:0: [sda] CDB: cdb[0]=0x88: 88 00 00 00 00 07 22 50 bc e0 00 00 01 00 00 00 end_request: I/O error, dev sda, sector 30640487648 But all disk are in Firmware state: Online, Spun Up. Also there is not a single ATA read or write error in any disk in the raid (I check them with smartctl -a -d sat+megaraid,N -H /dev/sda). The only strange thing is in the output in megacli: megacli -LDInfo -L0 -a0 ... Bad Blocks Exist: Yes How could there be bad blocks in a Virtual Drive, which is in optimal state and no disk is broken or even with a single error? I tried "Consistency Check", but it finished successfully and the errors are still in dmesg. Could Someone help me to figure it out what is wrong with my raid?