Databáze řešení

Introduction

This article how to use a software RAID for organizing the interaction of multiple drives in a Linux operating system, and without using an hardware RAID controller.

Servers with more than two drives, which you ordered together with an operating system, or which you installed via Progressive Robot, are already pre-configured with the recommended RAID level (1 or 6). Moreover, you can perform customizable Linux installations using our Installimage script in the Rescue System. You can use it to configure several RAID levels as well. And you can combine software RAID with LVM.

Display the state of a software RAID

To do this, just use this command:

cat /proc/mdstat

If no RAID is active, the output looks like this:

Personalities : [raid1]
unused devices: <none>

Here's the output for a configured RAID1:

Personalities : [raid1]
md2 : active raid1 sda3[2] sdb3[1]
      234405504 blocks super 1.2 [2/2] [UU]
      bitmap: 0/2 pages [0KB], 65536KB chunk

md1 : active raid1 sda2[2] sdb2[1]
      523712 blocks super 1.2 [2/2] [UU]

md0 : active raid1 sda1[2] sdb1[1]
      33521664 blocks super 1.2 [2/2] [UU]

unused devices: <none>

Here's the output for a configured RAID0 (You need to always configure the /boot partition md0 as RAID1 to allow the server to boot from it):

Personalities : [raid1] [raid0]
md2 : active raid0 sda3[0] sdb3[1]
      883956736 blocks super 1.2 512k chunks

md1 : active raid0 sda2[0] sdb2[1]
      52393984 blocks super 1.2 512k chunks

md0 : active raid1 sda1[0] sdb1[1]
      523264 blocks super 1.2 [2/2] [UU]

unused devices: <none>

If there is a progress bar displayed under one of the partitions, a RAID resync is currently running:

md0 : active raid1 sdb1[0] sdc1[1]
     2095040 blocks super 1.2 [2/2] [UU]
     	[====>................]  resync = 32.7% (418656/2095040) finish=4.2min speed=131219K/sec

Add a software RAID array

In our example scenario, the drives /dev/sda and /dev/sdb are already combined in multiple RAID1 arrays, which contain the operating system:

cat /proc/mdstat
Personalities : [raid1]
md2 : active raid1 sda3[2] sdb3[1]
      234405504 blocks super 1.2 [2/2] [UU]
      bitmap: 0/2 pages [0KB], 65536KB chunk

md1 : active raid1 sda2[2] sdb2[1]
      523712 blocks super 1.2 [2/2] [UU]

md0 : active raid1 sda1[2] sdb1[1]
      33521664 blocks super 1.2 [2/2] [UU]

unused devices: <none>

But we have two more drives (/dev/sdc and /dev/sdd), which we would also like to set up for data storage with RAID1 array. So we need to add the RAID array first:

mdadm --create --verbose /dev/md3 --level=1 --raid-devices=2 /dev/sdc /dev/sdd

The RAID configuration should now look like this:

cat /proc/mdstat
Personalities : [raid1]
md3 : active raid1 sdc1[0] sdd1[1]
     2095040 blocks super 1.2 [2/2] [UU]
     	[====>................]  resync = 32.7% (418656/2095040) finish=4.2min speed=131219K/sec

md2 : active raid1 sda3[2] sdb3[1]
      234405504 blocks super 1.2 [2/2] [UU]
      bitmap: 0/2 pages [0KB], 65536KB chunk

md1 : active raid1 sda2[2] sdb2[1]
      523712 blocks super 1.2 [2/2] [UU]

md0 : active raid1 sda1[2] sdb1[1]
      33521664 blocks super 1.2 [2/2] [UU]

unused devices: <none>

Now we can format the new partition (here with EXT4) and mount them:

mkfs.ext4 /dev/md3
mount /dev/md3 /mnt

Email notification when a drive in software RAID fails

Requirement: You must first install and configure a mail server of your choice (e.g. Sendmail).

Debian/Ubuntu/CentOS

Edit /etc/mdadm/mdadm.conf or /etc/mdadm.conf (CentOS) and change the following line:

MAILADDR holu@example.com

Here you can directly specify a destination address. Or, you can forward all emails sent to root to a specific email address using /etc/aliases.

You can also optionally configure the sending email address:

MAILFROM mdadm@example.com

For Debian and Ubuntu, it is important that you set AUTOCHECK in the file /etc/default/mdadm to true:

# grep AUTOCHECK= /etc/default/mdadm
AUTOCHECK=true

For CentOS, you must enable the RAID check in the file /etc/sysconfig/raid-check:

# grep ENABLED /etc/sysconfig/raid-check
ENABLED=yes

openSUSE

Edit /etc/sysconfig/mdadm and add the email address where you would receive the notification next to the variable MDADM_MAIL:

MDADM_MAIL="holu@example.com"

Test the configuration

You can verify your configuration by letting mdadm send a test mail to the mail address using this command:

mdadm --monitor --test --oneshot /dev/md0

You should also ensure that the file /etc/cron.daily/mdadm contains the following line, which performs the daily monitoring of your RAID:

exec --monitor --scan --oneshot

Removing a software RAID

To remove a software RAID, you can use the following commands. If you are doing this for the system partitions, we recommend that you boot the server to the Rescue System:

mdadm --remove /dev/md0
mdadm --remove /dev/md1
mdadm --remove /dev/md2

mdadm --stop /dev/md0
mdadm --stop /dev/md1
mdadm --stop /dev/md2

After that, you can formatt the drives normally again (for example, with EXT4):

mkfs.ext4 /dev/sda
mkfs.ext4 /dev/sdb

You can check the result with the commands...

cat /proc/mdstat

...and...

fdisk -l

And now you should remove the software RAID.