Software RAID with mdadm - Revision history

Michael: /* Moving the RAID disks to a new system */

2013-11-18T17:02:12Z

Moving the RAID disks to a new system

Roshan: /* Moving the RAID disks to a new system */

2012-11-06T11:11:23Z

Moving the RAID disks to a new system

Roshan: /* Moving the RAID disks to a new system = */

2012-11-06T11:10:19Z

Moving the RAID disks to a new system =

Roshan: /* Copy drive partition information */

2012-11-06T11:10:06Z

Copy drive partition information

David at 09:35, 2 July 2012

2012-07-02T09:35:26Z

David: Created page with "===== Create a new RAID array ===== Create (mdadm --create) is used to create a new array: mdadm --create --verbose /dev/md0 --level=1 /dev/sda1 /dev/sdb2 # or using ..."

2012-07-02T09:13:46Z

Created page with "===== Create a new RAID array ===== Create (mdadm --create) is used to create a new array: <syntaxhighlight> mdadm --create --verbose /dev/md0 --level=1 /dev/sda1 /dev/sdb2 # or using ..."

New page

===== Create a new RAID array =====

Create (mdadm --create) is used to create a new array:

<syntaxhighlight>
mdadm --create --verbose /dev/md0 --level=1 /dev/sda1 /dev/sdb2
# or using the compact notation:
mdadm -Cv /dev/md0 -l1 -n2 /dev/sd[ab]1
</syntaxhighlight>

===== Create /etc/mdadm.conf =====

/etc/mdadm.conf is the main configuration file for mdadm. After we create our RAID arrays we add them to this file using:

<syntaxhighlight>
mdadm --detail --scan >> /etc/mdadm.conf
</syntaxhighlight>

===== Remove a disk from an array =====

We can’t remove a disk directly from the array, unless it is failed, so we first have to fail it (if the drive it is failed this is normally already in failed state and this step is not needed):

<syntaxhighlight>
mdadm --fail /dev/md0 /dev/sda1
</syntaxhighlight>

and now we can remove it:

<syntaxhighlight>
mdadm --remove /dev/md0 /dev/sda1
</syntaxhighlight>

This can be done in a single step using:

<syntaxhighlight>
mdadm /dev/md0 --fail /dev/sda1 --remove /dev/sda1
</syntaxhighlight>

===== Add a disk to an existing array =====

We can add a new disk to an array (replacing a failed one probably):

<syntaxhighlight>
mdadm --add /dev/md0 /dev/sdb1
</syntaxhighlight>

===== Verifying the status of the RAID arrays =====

We can check the status of the arrays on the system with:

<syntaxhighlight>
cat /proc/mdstat
# or
mdadm --detail /dev/md0

[user@localhost:]$ cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sdb1[1] sda1[0]
104320 blocks [2/2] [UU]

md1 : active raid1 sdb3[1] sda3[0]
19542976 blocks [2/2] [UU]

md2 : active raid1 sdb4[1] sda4[0]
223504192 blocks [2/2] [UU]
</syntaxhighlight>

here we can see both drives are used and working fine – U. A failed drive will show as F, while a degraded array will miss the second disk -

'''Note:''' while monitoring the status of a RAID rebuild operation using watch can be useful:
<syntaxhighlight>
watch cat /proc/mdstat
</syntaxhighlight>

===== Stop and delete a RAID array =====

If we want to completely remove a raid array we have to stop if first and then remove it:

<syntaxhighlight>
mdadm --stop /dev/md0
mdadm --remove /dev/md0
</syntaxhighlight>

and finally we can even delete the superblock from the individual drives:

<syntaxhighlight>
mdadm --zero-superblock /dev/sda
</syntaxhighlight>

Finally in using RAID1 arrays, where we create identical partitions on both drives this can be useful to copy the partitions from sda to sdb:

<syntaxhighlight>
sfdisk -d /dev/sda | sfdisk /dev/sdb
</syntaxhighlight>

===== Example of RAID6 across 24 Drives =====

'''Note''': All the drives need to have the same partition information

In this example sda is the OS and is ignored.

Script to create all the partitions:
<syntaxhighlight>
#!/bin/bash

count=0;
for i in `ls /dev/sd*`
do

# ignore sda, sda1 and sda2
if [ $count -lt 3 ]
then
echo "skipping sda"
else
parted $i -- mklabel msdos
parted $i -- mkpart primary 0 -0
fi

count=`echo "$count +1"|bc`;

done
</syntaxhighlight>

Create the array (sdb1, sdc1 ... sdy1)
<syntaxhighlight>
mdadm -Cv /dev/md0 -l6 -n24 /dev/sd[b-y]1
</syntaxhighlight>

Create the filesystem on md0 (STFC args)
<syntaxhighlight>
[root@localhost MegaCli]$ mkfs.xfs -f -l version=2 -i size=1024 -n size=65536 -L raid6 /dev/md0
meta-data=/dev/md0 isize=1024 agcount=32, agsize=167678704 blks
= sectsz=4096 attr=0
data = bsize=4096 blocks=5365718336, imaxpct=25
= sunit=16 swidth=352 blks, unwritten=1
naming =version 2 bsize=65536
log =internal log bsize=4096 blocks=32768, version=2
= sectsz=4096 sunit=1 blks, lazy-count=0
realtime =none extsz=1441792 blocks=0, rtextents=0
</syntaxhighlight>

===== Copy drive partition information =====
If you need to copy drive partition information, use <tt>sfdisk</tt>
<syntaxhighlight>
# e.g clone sdc with partition info from sda
[root@compute00 ~]$ sfdisk -d /dev/sda > partition_info.pt
[root@compute00 ~]$ sfdisk /dev/sdc < partition_info.pt
</syntaxhighlight>

← Older revision		Revision as of 17:02, 18 November 2013
Line 157:		Line 157:

	we can then mount it as any other disk using /dev/md[n] name		we can then mount it as any other disk using /dev/md[n] name
		+
		+
		+	You may need to set up thje config file first:
		+
		+	<syntaxhighlight>
		+	echo DEVICE /dev/sd{a,b,c} > /etc/mdadm.conf
		+	mdadm --detail --scan >> /etc/mdadm.conf
		+	</syntaxhighlight>

← Older revision		Revision as of 11:11, 6 November 2012
Line 155:		Line 155:
	mdadm will identify and assemble the RAID with following cmd.		mdadm will identify and assemble the RAID with following cmd.
	<syntaxhighlight> sudo mdadm --assemble --scan </syntaxhighlight>		<syntaxhighlight> sudo mdadm --assemble --scan </syntaxhighlight>
		+
		+	we can then mount it as any other disk using /dev/md[n] name

@@ Line 150: / Line 150: @@
-==== Moving the RAID disks to a new system =====
+==== Moving the RAID disks to a new system ====
 Connect the RAID disk to a the new system.
 mdadm will identify and assemble the RAID with following cmd.
 <syntaxhighlight> sudo mdadm --assemble --scan </syntaxhighlight>

← Older revision		Revision as of 11:10, 6 November 2012
Line 148:		Line 148:
	[root@compute00 ~]$ sfdisk /dev/sdc < partition_info.pt		[root@compute00 ~]$ sfdisk /dev/sdc < partition_info.pt
	</syntaxhighlight>		</syntaxhighlight>
		+
		+
		+	==== Moving the RAID disks to a new system =====
		+
		+	Connect the RAID disk to a the new system.
		+	mdadm will identify and assemble the RAID with following cmd.
		+	<syntaxhighlight> sudo mdadm --assemble --scan </syntaxhighlight>

@@ Line 4: / Line 4: @@
 <syntaxhighlight>
-mdadm --create --verbose /dev/md0 --level=1 /dev/sda1 /dev/sdb2
+mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2 /dev/sda1 /dev/sdb2
 # or using the compact notation:
 mdadm -Cv /dev/md0 -l1 -n2 /dev/sd[ab]1