linux software raid 5 quick guide

Here will create a raid 5 setup with three drives for redundant storage using mdadm (not raidtools). This example does not include putting your O.S. root partion on the raid device. It is only for a volume to be mounted by Linux which boots off of another device.

Number of drives: 3

Number of spare drives: 0

All drives same size

All space used on all drives

devices to be used in this example: sdb sdc sdd

Versions

Versions in use for the kernel and mdadm on the linux device in this example...

kernel: 3.10.17 mdadm: v3.2.6 - 25th October 2012

kernel config

Check for support If your system has RAID support, you should have a file called /proc/mdstat. If you do not have that file, maybe your kernel does not have RAID support. For more info on configuring your linux kernel for software raid, go here

prepare disks

check existing partition tables

this command will dump the partitions for all three drives

# fdisk -l /dev/sd[bcd]

Assumming you have 3 drives with no data to preserve or they are new, delete any existing partions in preparation for creating new partitions of type "Linux raid autodetect"

create three raid partions

assuming they don't already exist...

linux # fdisk /dev/sdb

The device presents a logical sector size that is smaller than
the physical sector size. Aligning to a physical sector (or optimal
I/O) size boundary is recommended, or performance may be impacted.
Welcome to fdisk (util-linux 2.22.2).

Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): n
Partition type:
  p   primary (0 primary, 0 extended, 4 free)
  e   extended
Select (default p): 
Using default response p
Partition number (1-4, default 1): 
Using default value 1
First sector (2048-1953525167, default 2048): 
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-1953525167, default 1953525167): 
Using default value 1953525167
Partition 1 of type Linux and of size 931.5 GiB is set

Command (m for help): t
Selected partition 1
Hex code (type L to list codes): fd
Changed system type of partition 1 to fd (Linux raid autodetect)

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.

Duplicate the sdb partition tables to sdc and sdd. You can re-run fdisk two more times, or just run this.

# sfdisk -d /dev/sdb | sfdisk /dev/sdc; sfdisk -d /dev/sdb | sfdisk /dev/sdd

Verify the partition layout

Partitions should look similar to the following:

# fdisk -l /dev/sd[bcd] | grep -A 1 Device
  Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048  1953525167   976761560   fd  Linux raid autodetect
--
  Device Boot      Start         End      Blocks   Id  System
/dev/sdc1            2048  1953525167   976761560   fd  Linux raid autodetect
--
  Device Boot      Start         End      Blocks   Id  System
/dev/sdd1            2048  1953525167   976761560   fd  Linux raid autodetect

Creating an array

# mdadm --create /dev/md0 --level=5 --raid-devices=3 /dev/sdb1 /dev/sdc1 /dev/sdd1

verify the creation

# cat /proc/mdstat 
Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] [multipath] [faulty] 
md0 : active raid5 sdd1[3] sdc1[1] sdb1[0]
     1953260544 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/2] [UU_]
     [>....................]  recovery =  0.1% (1143808/976630272) finish=312.6min speed=51991K/sec

if you see something similar to above you are OK. the recover = xx.x% is the initial building of the parity data I believe.

if you care to watch / monitor the sync in a terminal

# while true; do cat /proc/mdstat | grep recovery; sleep 300; done

create and mount filesystem

# mkfs.ext4 /dev/md0

# mount /dev/md0 /mnt/mysuperraidvolume

add the /etc/fstab entry line to mount on boot

/dev/md0                /vol1           ext4            defaults        0 0

checking status

# mdadm --detail /dev/md127
/dev/md127:
       Version : 1.2
 Creation Time : Tue Aug  5 07:35:04 2014
    Raid Level : raid5
    Array Size : 1953260544 (1862.77 GiB 2000.14 GB)
 Used Dev Size : 976630272 (931.39 GiB 1000.07 GB)
  Raid Devices : 3
 Total Devices : 3
   Persistence : Superblock is persistent

   Update Time : Sat Jun 11 16:37:45 2016
         State : clean 
Active Devices : 3
Working Devices : 3
Failed Devices : 0
 Spare Devices : 0

        Layout : left-symmetric
    Chunk Size : 512K

          Name : nasser:0  (local to host nasser)
          UUID : 3733be79:728f962f:ffe10ec0:ce451bb3
        Events : 28933

   Number   Major   Minor   RaidDevice State
      0       8       17        0      active sync   /dev/sdb1
      1       8       33        1      active sync   /dev/sdc1
      3       8       49        2      active sync   /dev/sdd1

Links

this guide is recommended by the linux kernel help... [Software RAID HOWTO]