Hotplug

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(mdadm versions < 3.1.2)
(mdadm versions < 3.1.2)
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We see that sda1 has role '''[2]'''. Since RAID1 needs only 2 components - [0] and [1], the [2] means "Spare disk". And it is '''(F)'''ailed.
 
We see that sda1 has role '''[2]'''. Since RAID1 needs only 2 components - [0] and [1], the [2] means "Spare disk". And it is '''(F)'''ailed.
  
But why the system thinks that sda2 is still OK?
+
But why the system thinks that /dev/sda2 in /dev/md1 is still OK?
Because my system haven't tried to access /dev/md1 yet (I have no data on /dev/md1). The /dev/sda2 will be marked as fault automatically as soon as I try to access /dev/md1:
+
Because my system hasn't tried to access /dev/md1 yet (I have no data on /dev/md1). The /dev/sda2 will be marked as fault automatically as soon as I try to access /dev/md1:
  
 
  # dd if=/dev/md1 of=/dev/null bs=1 count=1
 
  # dd if=/dev/md1 of=/dev/null bs=1 count=1

Revision as of 07:33, 15 April 2010

HW issues of the disk hotplugging are described in the Hotswap chapter of theHardware issues page.

The Linux RAID supports hotplug operations fully from Hot-unplug branch of the mdadm version 3.1.2.

mdadm versions < 3.1.2

Let's have the following RAID configuration:

# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sda1[0] sdb1[1]
      3903680 blocks [2/2] [UU]

md1 : active raid1 sda2[0] sdb2[1]
      224612672 blocks [2/2] [UU]

The md0 contains the system, md1 is for data (but is not used yet).

If we hot-unplug the disk /dev/sda, the /proc/mdstat will show:

# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sda1[2](F) sdb1[1]
      3903680 blocks [2/1] [_U]

md1 : active raid1 sda2[0] sdb2[1]
      224612672 blocks [2/2] [UU]

We see that sda1 has role [2]. Since RAID1 needs only 2 components - [0] and [1], the [2] means "Spare disk". And it is (F)ailed.

But why the system thinks that /dev/sda2 in /dev/md1 is still OK? Because my system hasn't tried to access /dev/md1 yet (I have no data on /dev/md1). The /dev/sda2 will be marked as fault automatically as soon as I try to access /dev/md1:

# dd if=/dev/md1 of=/dev/null bs=1 count=1
1+0 records in
1+0 records out
1 byte (1 B) copied, 0.0184819 s, 0.1 kB/s
# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sda1[2](F) sdb1[1]
      3903680 blocks [2/1] [_U]

md1 : active raid1 sda2[2](F) sdb2[1]
      224612672 blocks [2/1] [_U]


What we can do is remove the failed disk:

# mdadm /dev/md0 --fail detached --remove detached
mdadm: hot removed 8:1

mdadm versions > 3.1.2

(to be finished)

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