Setting up a software RAID array
This document will show how to create hard disk mirroring using cheap IDE disks.
This document was written for alpine-1.3.8 or later. It is tested with alpine-1.7.3.
I will setup 2 raid devices, md0 for swap and md1 for data. I use swap on a raid1 for maximum reliability. If you prefer maximum speed, you don't need configure any raid devices for swap. Just add 2 swap partitions on different disks and linux will stripe them automatically. The downside is that at the moment one disk fails, the system will go down. Thats why I choose to put the swap on raid1.
Loading needed modules
Start with loading the ide-disk and raid1 kernel modules. If you use SATA or SCSI disks you will not need the ide-disk module.
modprobe ide-disk modprobe raid1
Add them to /etc/modules so they get loaded during next reboot.
echo ide-disk >> /etc/modules echo raid1 >> /etc/modules
Creating the partitions
I will use /dev/hde and /dev/hdg in this document but you will probably use /dev/hda and /dev/hdc. Note that the disks should not be connected on the same IDE bus (sharing the same IDE cable). To find what disks you have available, look in /proc/partitions or look at the /dev/disk* links that the mdev system has created.
~ $ ls -l /dev/disk* lrwxrwxrwx 1 root root 3 Aug 24 12:49 /dev/disk -> hde lrwxrwxrwx 1 root root 3 Aug 24 12:49 /dev/disk0 -> hde lrwxrwxrwx 1 root root 3 Aug 24 12:49 /dev/disk1 -> hdg
Create the partitions using fdisk.
I will use 512MB for swap and the rest for /var. My partition table looks like this:
Device Boot Start End Blocks Id System /dev/hde1 1 992 499936+ fd Linux raid autodetect /dev/hde2 993 77545 38582712 fd Linux raid autodetect
Remeber to set the type (with 't' in fdisk) to Linux raid autodetect. (fd)
Do the same with your second disk.
Mine looks like this:
Device Boot Start End Blocks Id System /dev/hdg1 1 992 499936+ fd Linux raid autodetect /dev/hdg2 993 77545 38582712 fd Linux raid autodetect
== Setting up the raid array Install mdadm to set up the arrays.
mknod /dev/md0 b 9 0 mknod /dev/md1 b 9 1
Create the arrays.
mdadm --create -l 1 -n 2 /dev/md0 /dev/hde1 /dev/hdg1 mdadm --create -l 1 -n 2 /dev/md1 /dev/hde2 /dev/hdg2
Monitorin sync status
You should now be able to see the array syncronize by looking at the contents of /proc/mdstat.
~ $ cat /proc/mdstat Personalities : [raid1] md1 : active raid1 hdg2 hde2 38582592 blocks [2/2] [UU] [==>..................] resync = 10.5% (4056192/38582592) finish=68.5min speed=8388K/sec md0 : active raid1 hdg1 hde1 499840 blocks [2/2] [UU] unused devices: <none>
You don't need to wait til it is fully syncronized to continue.
Create the /etc/mdadm.conf file so mdadm knows how your raid setup is:
mdadm --detail --scan > /etc/mdadm.conf
To make sure the raid devices start during the next reboot run:
rc_add -s 10 -k mdadm-raid
The ~~-s 10~~ option is to make sure that the raid arrays are started early, before things like lvm and localmount.
Use lbu commit as usual to save configs to usb or floppy.
You should now be able to create swap on /dev/md0 and a filesystem on /dev/md1 using the ~~mkswap~~ and ~~mkfs.*~~ commands.