Hi Unixmen readers, I am Vishal Vyas, a Linux System Administrator from India. I am new here, so please be nice with me.
In this quick how-to, let us see how to setup Raid level 5 on Linux. For more details about RAID 5, please refer this link. Linux RAID 5 requires at least three disks.
Image credit: Wikipedia
First let us create 3 Partitions.
Create Partitions
To view the existing partitions use following command:
# fdisk -l
Sample output:
Device Boot Start End Blocks Id System /dev/sda1 * 1 13 102400 7 HPFS/NTFS Partition 1 does not end on cylinder boundary. /dev/sda2 13 12748 102294528 7 HPFS/NTFS /dev/sda3 12749 12773 200812+ 83 Linux /dev/sda4 12774 60802 385786880 5 Extended /dev/sda5 12774 12799 204800 83 Linux /dev/sda6 12799 19174 51200000 83 Linux /dev/sda7 19174 19429 2048000 82 Linux swap / Solaris
Now let us create three partions of each size 100MB using fdisk command
Use fdisk command to create and manage partitions
# fdisk /dev/sda WARNING: DOS-compatible mode is deprecated. It's strongly recommended to switch off the mode (command 'c') and change display units to sectors (command 'u').
To display existing partition table:
Command (m for help): p
Disk /dev/sda: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0xa54ba54b Device Boot Start End Blocks Id System /dev/sda1 * 1 13 102400 7 HPFS/NTFS Partition 1 does not end on cylinder boundary. /dev/sda2 13 12748 102294528 7 HPFS/NTFS /dev/sda3 12749 12773 200812+ 83 Linux /dev/sda4 12774 60802 385786880 5 Extended /dev/sda5 12774 12799 204800 83 Linux /dev/sda6 12799 19174 51200000 83 Linux /dev/sda7 19174 19429 2048000 82 Linux swap / Solaris
Now let us create three partions of each size 100MB using fdisk command.
To Create new partition press n and enter the size (ex.+100M).
Command (m for help): n First cylinder (19429-60802, default 19429): Using default value 19429 Last cylinder, +cylinders or +size{K,M,G} (19429-60802, default 60802): +100M
Command (m for help): n First cylinder (19443-60802, default 19443): Using default value 19443 Last cylinder, +cylinders or +size{K,M,G} (19443-60802, default 60802): +100M
Command (m for help): n First cylinder (19457-60802, default 19457): Using default value 19457 Last cylinder, +cylinders or +size{K,M,G} (19457-60802, default 60802): +100M
Change partition type
Press t to change the partition id of all the three partitions created by you to fd (linux raid auto).
Command (m for help): t Partition number (1-10): 8 Hex code (type L to list codes): fd Changed system type of partition 8 to fd (Linux raid autodetect)
Command (m for help): t Partition number (1-10): 9 Hex code (type L to list codes): fd Changed system type of partition 9 to fd (Linux raid autodetect)
Command (m for help): t Partition number (1-10): 10 Hex code (type L to list codes): fd Changed system type of partition 10 to fd (Linux raid autodetect)
To Show partition table, press P :
Command (m for help): p
Disk /dev/sda: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0xa54ba54b Device Boot Start End Blocks Id System /dev/sda1 * 1 13 102400 7 HPFS/NTFS Partition 1 does not end on cylinder boundary. /dev/sda2 13 12748 102294528 7 HPFS/NTFS /dev/sda3 12749 12773 200812+ 83 Linux /dev/sda4 12774 60802 385786880 5 Extended /dev/sda5 12774 12799 204800 83 Linux /dev/sda6 12799 19174 51200000 83 Linux /dev/sda7 19174 19429 2048000 82 Linux swap / Solaris /dev/sda8 19429 19442 111257+ fd Linux raid autodetect /dev/sda9 19443 19456 112423+ fd Linux raid autodetect /dev/sda10 19457 19470 112423+ fd Linux raid autodetect
Save the newly created partitions.
Command (m for help): wq [Save change]
The partition table has been altered! Calling ioctl() to re-read partition table.
Update the kernel to save the changes without restarting the system.
# partprobe Warning: WARNING: the kernel failed to re-read the partition table on /dev/sda (Device or resource busy). As a result, it may not reflect all of your changes until after reboot. Again we will check the existing partitions using fdisk command.
Again we will check the existing partitions using fdisk command
# fdisk -l
Sample output:
Device Boot Start End Blocks Id System
/dev/sda1 * 1 13 102400 7 HPFS/NTFS
Partition 1 does not end on cylinder boundary.
/dev/sda2 13 12748 102294528 7 HPFS/NTFS
/dev/sda3 12749 12773 200812+ 83 Linux
/dev/sda4 12774 60802 385786880 5 Extended
/dev/sda5 12774 12799 204800 83 Linux
/dev/sda6 12799 19174 51200000 83 Linux
/dev/sda7 19174 19429 2048000 82 Linux swap / Solaris
/dev/sda8 19429 19442 111257+ fd Linux raid autodetect
/dev/sda9 19443 19456 112423+ fd Linux raid autodetect
/dev/sda10 19457 19470 112423+ fd Linux raid autodetect.
Creating RAID 5 with these partitions
# mdadm --create /dev/md0 --level=5 --raid-devices=3 /dev/sda8 /dev/sda9 /dev/sda10 mdadm: Defaulting to version 1.2 metadata mdadm: array /dev/md0 started.
To see the details of raid use the following command:
# cat /proc/mdstat
Sample output:
Personalities : [raid6] [raid5] [raid4] md0 : active raid5 sda10[3] sda9[1] sda8[0] 222208 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/3] [UUU]
To show raid devices:
# mdadm --detail /dev/md0
Sample output:
/dev/md0: Version : 1.2 Creation Time : Thu Jan 30 19:41:32 2014 Raid Level : raid5 Array Size : 222208 (217.04 MiB 227.54 MB) Used Dev Size : 111104 (108.52 MiB 113.77 MB) Raid Devices : 3 Total Devices : 3 Persistence : Superblock is persistent Update Time : Thu Jan 30 19:41:42 2014 State : clean Active Devices : 3 Working Devices : 3 Failed Devices : 0 Spare Devices : 0 Layout : left-symmetric Chunk Size : 512K Name : localhost.localdomain:0 (local to host localhost.localdomain) UUID : a4caa02d:8e6fd77c:e83fcdea:d471cee6 Events : 18 Number Major Minor RaidDevice State 0 8 8 0 active sync /dev/sda8 1 8 9 1 active sync /dev/sda9 3 8 10 2 active sync /dev/sda10
Now Format file system for your RAID devices
# mkfs.ext4 /dev/md0
mke2fs 1.41.12 (17-May-2010) Filesystem label= OS type: Linux Block size=1024 (log=0) Fragment size=1024 (log=0) Stride=512 blocks, Stripe width=1024 blocks 55552 inodes, 222208 blocks 11110 blocks (5.00%) reserved for the super user First data block=1 Maximum filesystem blocks=67371008 28 block groups 8192 blocks per group, 8192 fragments per group 1984 inodes per group Superblock backups stored on blocks: 8193, 24577, 40961, 57345, 73729, 204801, 221185 Writing inode tables: done Creating journal (4096 blocks): done Writing superblocks and filesystem accounting information: done This filesystem will be automatically checked every 22 mounts or 180 days, whichever comes first. Use tune2fs -c or -i to override.
Mounting the RAID partition
Once you create all of your partitions as Software RAID partitions, you must create the RAID device and mount point.
# mkdir raid5 # mount /dev/md0 raid5
# df -h ## Command is used to see the space allocation ## Filesystem Size Used Avail Use% Mounted on /dev/sda6 49G 21G 28G 44% / tmpfs 999M 88K 999M 1% /dev/shm /dev/sda5 194M 28M 156M 16% /boot /dev/md0 211M 6.1M 194M 4% /root/raid5
Manage faulty raid devices
Let us damage any raid partitions.
# mdadm --manage /dev/md0 --fail /dev/sda9 mdadm: set /dev/sda9 faulty in /dev/md0
Removing raid devices
# mdadm --manage /dev/md0 --remove /dev/sda9 mdadm: hot removed /dev/sda9 from /dev/md0
Adding raid devices
# mdadm --manage /dev/md0 --add /dev/sda9 mdadm: added /dev/sda9
View failed and working raid devices
# cat /proc/mdstat Personalities : [raid6] [raid5] [raid4] md0 : active raid5 sda9[4] sda10[3] sda8[0] 222208 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/3] [UUU] unused devices:
To remove the RAID follow these steps: –
1) unmount the mounted directory where raid is mounted.
# umount data/
2) Stop the device
# mdadm --stop /dev/md0 mdadm: stopped /dev/md0
3) View the details of your raid level using following command: –
# cat /proc/mdstat # mdadm --detail /dev/md0
