Create a dummy file in Linux.

This is a one liner to create a dummy file in Linux/Unix for testing purpose:

 dd if=/dev/zero of=dummyfile1.txt bs=1234567801 count=1

-rw-r--r-- 1 root root 1234567801 Feb 25 05:16 dummyfile1.txt


[root@RHEL5 ~]# du -sh dummyfile1.txt
1.2G    dummyfile1.txt

Creating RAID 5 with LVM and testing the disk failure.

Create 4 disks  of same size. scan the bus, run the fdisk -l command to view the newly created partitions
and follow the blog for the next steps.......

[root@RHEL5 ~]# echo "- - -" >  /sys/class/scsi_host/host0/scan

[root@RHEL5 ~]# fdisk -l

Disk /dev/sda: 21.4 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1         382     3068383+  83  Linux
/dev/sda2             383        1019     5116702+  83  Linux
/dev/sda3            1020        1503     3887730   83  Linux
/dev/sda4            1504        2610     8891977+   5  Extended
/dev/sda5            1504        1885     3068383+  83  Linux
/dev/sda6            1886        2076     1534176   82  Linux swap / Solaris
/dev/sda7            2077        2203     1020096   83  Linux
/dev/sda8            2204        2241      305203+  83  Linux

Disk /dev/sdb: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/sdb doesn't contain a valid partition table

Disk /dev/sdc: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/sdc doesn't contain a valid partition table

Disk /dev/sdd: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/sdd doesn't contain a valid partition table
[root@RHEL5 ~]#


------------------------------------------------------------

[root@RHEL5 ~]# mdadm --create --verbose /dev/md0 --level=5 --raid-devices=3 /dev/sdb /dev/sdc /dev/sdd
mdadm: layout defaults to left-symmetric
mdadm: chunk size defaults to 64K
mdadm: size set to 1048512K
mdadm: array /dev/md0 started.

------------------------------------------------------------

[root@RHEL5 ~]# mdadm --detail /dev/md0
/dev/md0:
        Version : 00.90.03
  Creation Time : Mon Feb 25 04:13:51 2013
     Raid Level : raid5
     Array Size : 2097024 (2048.22 MiB 2147.35 MB)
    Device Size : 1048512 (1024.11 MiB 1073.68 MB)
   Raid Devices : 3
  Total Devices : 3
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Mon Feb 25 04:13:51 2013
          State : clean, degraded, recovering
 Active Devices : 2
Working Devices : 3
 Failed Devices : 0
  Spare Devices : 1

         Layout : left-symmetric
     Chunk Size : 64K

 Rebuild Status : 83% complete

           UUID : a1ed8a09:8b0a0913:c2f6d8b1:5c67dfeb
         Events : 0.1

    Number   Major   Minor   RaidDevice State
       0       8       16        0      active sync   /dev/sdb
       1       8       32        1      active sync   /dev/sdc
       3       8       48        2      spare rebuilding   /dev/sdd


------------------------------------------------------------

[root@RHEL5 ~]# mdadm --detail /dev/md0
/dev/md0:
        Version : 00.90.03
  Creation Time : Mon Feb 25 04:13:51 2013
     Raid Level : raid5
     Array Size : 2097024 (2048.22 MiB 2147.35 MB)
    Device Size : 1048512 (1024.11 MiB 1073.68 MB)
   Raid Devices : 3
  Total Devices : 3
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Mon Feb 25 04:14:29 2013
          State : clean
 Active Devices : 3
Working Devices : 3
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 64K

           UUID : a1ed8a09:8b0a0913:c2f6d8b1:5c67dfeb
         Events : 0.2

    Number   Major   Minor   RaidDevice State
       0       8       16        0      active sync   /dev/sdb
       1       8       32        1      active sync   /dev/sdc
       2       8       48        2      active sync   /dev/sdd


------------------------------------------------------------

[root@RHEL5 ~]# pvcreate  /dev/md0
  Physical volume "/dev/md0" successfully created

[root@RHEL5 ~]# vgcreate lvm-raid /dev/md0
  Volume group "lvm-raid" successfully created

------------------------------------------------------------

[root@RHEL5 ~]# vgs
  VG       #PV #LV #SN Attr   VSize VFree
  lvm-raid   1   0   0 wz--n- 2.00G 2.00G

[root@RHEL5 ~]# pvs
  PV         VG       Fmt  Attr PSize PFree
  /dev/md0   lvm-raid lvm2 a-   2.00G 2.00G


------------------------------------------------------------

 Free  PE / Size       511 / 2.00 GB


[root@RHEL5 ~]# lvcreate -L 511 lvm-raid -n lvm0
  /dev/cdrom: open failed: Read-only file system
  Rounding up size to full physical extent 512.00 MB
  Logical volume "lvm0" created


------------------------------------------------------------

[root@RHEL5 /]# mke2fs -j /dev/lvm-raid/lvm0
mke2fs 1.39 (29-May-2006)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
131072 inodes, 524288 blocks
26214 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=67633152
64 block groups
8192 blocks per group, 8192 fragments per group
2048 inodes per group
Superblock backups stored on blocks:
        8193, 24577, 40961, 57345, 73729, 204801, 221185, 401409

Writing inode tables: done
Creating journal (16384 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 39 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

------------------------------------------------------------

[root@RHEL5 /]# mount /dev/lvm-raid/lvm0 /data/
[root@RHEL5 /]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1             2.9G  262M  2.5G  10% /
tmpfs                 506M     0  506M   0% /dev/shm
/dev/sda8             289M   11M  264M   4% /home
/dev/sda2             4.8G  138M  4.4G   4% /opt
/dev/sda7             965M   18M  898M   2% /tmp
/dev/sda5             2.9G  2.2G  531M  81% /usr
/dev/sda3             3.6G  124M  3.3G   4% /var
/dev/mapper/lvm--raid-lvm0
                      496M   19M  452M   4% /data

------------------------------------------------------------

Take the /dev/sdb out of the raid array.

[root@RHEL5 /]# mdadm /dev/md0 -f /dev/sdb
mdadm: set /dev/sdb faulty in /dev/md0
[root@RHEL5 /]# mdadm --detail /dev/md0
/dev/md0:
        Version : 00.90.03
  Creation Time : Mon Feb 25 04:13:51 2013
     Raid Level : raid5
     Array Size : 2097024 (2048.22 MiB 2147.35 MB)
    Device Size : 1048512 (1024.11 MiB 1073.68 MB)
   Raid Devices : 3
  Total Devices : 3
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Mon Feb 25 04:35:37 2013
          State : clean, degraded
 Active Devices : 2
Working Devices : 2
 Failed Devices : 1
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 64K

           UUID : a1ed8a09:8b0a0913:c2f6d8b1:5c67dfeb
         Events : 0.4

    Number   Major   Minor   RaidDevice State
       0       0        0        0      removed
       1       8       32        1      active sync   /dev/sdc
       2       8       48        2      active sync   /dev/sdd

       3       8       16        -      faulty spare   /dev/sdb


--------------------------------------------------------------

[root@RHEL5 /]# echo "- - -" > /sys/class/scsi_host/host0/scan
[root@RHEL5 /]# fdisk -l

Disk /dev/sda: 21.4 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1         382     3068383+  83  Linux
/dev/sda2             383        1019     5116702+  83  Linux
/dev/sda3            1020        1503     3887730   83  Linux
/dev/sda4            1504        2610     8891977+   5  Extended
/dev/sda5            1504        1885     3068383+  83  Linux
/dev/sda6            1886        2076     1534176   82  Linux swap / Solaris
/dev/sda7            2077        2203     1020096   83  Linux
/dev/sda8            2204        2241      305203+  83  Linux

Disk /dev/md0: 2147 MB, 2147352576 bytes
2 heads, 4 sectors/track, 524256 cylinders
Units = cylinders of 8 * 512 = 4096 bytes

Disk /dev/md0 doesn't contain a valid partition table

Disk /dev/sdb: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/sdb doesn't contain a valid partition table

Disk /dev/sdc: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/sdc doesn't contain a valid partition table

Disk /dev/sdd: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/sdd doesn't contain a valid partition table

Disk /dev/sde: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/sde doesn't contain a valid partition table

Noe lets add the newly created device in the array.

--------------------------------------------------------------

[root@RHEL5 /]# mdadm /dev/md0 -a /dev/sde
mdadm: added /dev/sde


See the output the device is seen:

[root@RHEL5 /]# mdadm --detail /dev/md0
/dev/md0:
        Version : 00.90.03
  Creation Time : Mon Feb 25 04:13:51 2013
     Raid Level : raid5
     Array Size : 2097024 (2048.22 MiB 2147.35 MB)
    Device Size : 1048512 (1024.11 MiB 1073.68 MB)
   Raid Devices : 3
  Total Devices : 4
Preferred Minor : 0
    Persistence : Superblock is persistent


    Update Time : Mon Feb 25 04:41:01 2013
          State : clean
 Active Devices : 3
Working Devices : 3
 Failed Devices : 1
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 64K

           UUID : a1ed8a09:8b0a0913:c2f6d8b1:5c67dfeb
         Events : 0.6

    Number   Major   Minor   RaidDevice State
       0       8       64        0      active sync   /dev/sde
       1       8       32        1      active sync   /dev/sdc
       2       8       48        2      active sync   /dev/sdd

       3       8       16        -      faulty spare   /dev/sdb


--------------------------------------------------------------

Thanks.