Linux software raid notes

Here are a few other notes on linux software raid. I created a directory called raidinfo to keep information in to make it easy to maintain the raid array. First... from the software raid howto, I've done the following....

sfdisk -d /dev/hda > /raidinfo/partitions.hda
sfdisk -d /dev/hde > /raidinfo/partitions.hde

So.... I've now got a good snapshot of the partitioning data. When I hooked up an external usb drive to add to the array, all I needed to do is this...

sfdisk /dev/sda < /raidinfo/partitions.hda

And.... I've got the drive partitioned.

Then I did a quick .... sudo mdadm --grow /dev/md0 -n 3 (previously 2)
and sudo mdadm --add /dev/md0 /dev/sda1

(for each partition and md0 device and things were happily syncing.) Actually, I've done a script to grow and add the partitions to the arrays and then to remove and "shrink" the array *(tip: - use the grow command with -n 2 to shrink.)

The master boot record is another issue (grub is used on this system.) I found a hint about grub's batch mode and did a quick try of the following....

#!/bin/bash

cat <<EOF | /sbin/grub --batch

device (hd0) /dev/sda

root (hd0,0)

setup (hd0)

quit

EOF

which seemed to do the trick, things are still syncing (/boot had already finished though.) I'll test once the sync is finished.

The software raid and grub how-to is excellent by the way...

The only other thing left seems to be to update the /etc/mdadm/mdadm.conf file...

cd /etc/mdadm

cp mdadm.conf mdadm.conf.`date +%y%m%d`

echo "DEVICE partitions" > mdadm.conf

mdadm --detail --scan >> mdadm.conf