first confirm the device i/e sdb or sdc
fdisk -l
Command to read raw data from partition and create one file which will conatin that raw data information
## will try to read 35MB raw data from sdb partition and it will create test.read.out file.
[root@localhost tmp]# dd if=/dev/sdb of=test-read.out bs=1M count=35
dd: reading `/dev/sdb': Input/output error
29+1 records in
29+1 records out
30932992 bytes (31 MB) copied, 0.528385 seconds, 58.5 MB/s
## before creating a datastore run this command on blank partition / lun, don't run this command if we have already created a datastore , this command will write zero on sdb partition till 35MB.
[root@localhost tmp]# dd if=/dev/zero of=/dev/sdb bs=1M count=35
35+0 records in
35+0 records out
36700160 bytes (37 MB) copied, 0.334465 seconds, 110 MB/s
[root@localhost tmp]#