How to rebuild a software RAID

combilli · 02-10-2007, 12:12 PM

I've carelessly broke a software RAID 1 by deleting the partitions on 1 of the harddisk.

So the software raid is broken.

The system is still running.
And I want to rebuild the formatted harddisk and make the RAID1 running again ,which command should I use and how can I use it?

macemoneta · 02-10-2007, 03:36 PM

It actually takes two commands.

I'll assume the good RAID-1 disk partition is /dev/hda1, the drive that was formatted is /dev/hdb, and the RAID-1 device is /dev/md0. As root:

1. Partition /dev/hdb the same as /dev/hda:

sfdisk -d /dev/hda | sfdisk /dev/hdb

2. Add the partition to the array:

mdadm /dev/md0 --add /dev/hdb1

You can verify that it is syncing up with:

cat /proc/mdstat

combilli · 02-20-2007, 08:16 AM

Do I need to stop all server when I run the command mdadm?
that server was running dhcp....

macemoneta · 02-20-2007, 08:22 AM

The synchronization is a background process; there will be no impact to the running system.

combilli · 02-20-2007, 08:41 AM

Thanks. I'm rebuilding the data partition now...

And it's working good.

If the system is for mail server, when server getting email, does it impact the sync?

macemoneta · 02-20-2007, 12:09 PM

The sync will give priority to activity on the server. There is a minimum and maximum setting:

Code:

# cat /proc/sys/dev/raid/speed_limit_max 
200000
# cat /proc/sys/dev/raid/speed_limit_min 
1000

The minimum insures that the sync continues, even if the system is busy. You don't normally need to change the values, but you can via, for example:

echo "10000" > /proc/sys/dev/raid/speed_limit_max

Any changes take effect immediately.