Setting up a /var partition on software IDE raid1

2009-07-31T13:51:24Z

Belousa: /* Create filesystem */

This document wil show how to create harddisk mirroring using cheap IDE disks.

This document was written for alpine-1.3.8

I will setup swap on a raid1 for maximum reliability. If you prefer maximum speed, you don't need configure any raid devces 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.

== Setting up the RAID ==
Set up a raid array as described [[Setting up a software raid1 array|here]].
In this document two raid arrays are configured: md0 for swap (512MB) and md1 for /var.

It is generally a good idea to use LVM so you are able to easily extend your data storage in future. LVM is not discussed here.

== Create filesystem ==
Now we can creat swapspace and the filesystem for /var.
mkswap /dev/md0
swapon /dev/md0

You can verify that swap was really activated with ''free''. It should display how much swapspace you have.
free

We need to install the software to create the filesystem ("format" the partition). I will use '''ext3''' here so I install ''e2fsprogs''. If you prefer reiserfs or xfs you will have to install ''xfsprogs'' or ''reiserfsprogs'' instead.
apk_add e2fsprogs

If you use an Alpine release older than 1.3.8 you will need to manuall create a link to /etc/mtab.
ln -fs /proc/mounts /etc/mtab

Create the filesystem. The -j option makes it ext'''3'''. Without the -j option it will become non-journaling ext'''2'''. This step might take some time if your partition is big.
mke2fs -j /dev/md1

Now edit /etc/fstab and add your new partitions. Mine looks like this:
none /proc proc defaults 0 0
none /sys sysfs defaults 0 0
udev /dev tmpfs size=100k 0 0
none /dev/pts devpts defaults 0 0
tmpfs /dev/shm tmpfs defaults 0 0
/dev/cdrom /media/cdrom iso9660 ro 0 0
/dev/fd0 /media/floppy vfat noauto 0 0
/dev/usba1 /media/usb vfat noauto 0 0
none /proc/bus/usb usbfs noauto 0 0

/dev/md0 swap swap defaults 0 0
/dev/md1 /var ext3 defaults 0 0

== Move the data ==
Now you should stop all services running that put anything in /var (syslog for example). If you have booted on a clean installation and not run setup-alpine, then no services should be running. However, some packages might have created dirs in /var so we need to backup /var mount the new and move all backed up dirs back to the raided /var.

mv /var /var.tmp
mkdir /var
mount /var
mv /var.tmp/* /var
rmdir /var.tmp

Verify that everyting looks ok with the ''df'' utility.
~ $ df
Filesystem 1k-blocks Used Available Use% Mounted on
none 255172 23544 231628 9% /
udev 100 0 100 0% /dev
/dev/cdrom 142276 142276 0 100% /media/cdrom
/dev/md1 37977060 181056 35866876 1% /var

== Survive reboots ==
Now we have everyting up and running. We need to make sure that everything will be restored during next reboot.

Create an initscript that will mount /var for you during boot. I call it /etc/init.d/mountdisk and it looks like this:
#!/sbin/runscript

start() {
ebegin "Mounting /var"
mount /var
eend $?
}

stop() {
ebegin "Unmounting /var"
umount /var
eend $?
}

Make it exectutable:
chmod +x /etc/init.d/mountdisk

'''NOTE:''' Since Alpine-1.7.3 there is a ''localmount'' script shipped so you will not need to create your own ''mountdisk'' script.

And that /var is mounted *after* raid is created. The -k option will make alpine to unmount the /Var partition during boot. Also add start of swap too boot
rc_add -k -s 06 mountdisk
rc_add -k -s 06 swap

The /dev/md* device nodes will not be created automatically so we need to put the on floppy too.
lbu include /dev/md*

If you have users on the server and want the /home be permantent you can create a directory /var/home and create links to /var/home.
mkdir /var/home
mv /home/* /var/home/
ln -s /var/home/* /home/

'''NOTE:''' You cannot just replace /home with a link that points to /var/home since the base has a director /home. When the boot tries to copy the config from floppy it will fail because of the already existing /home directory.

Make sure the links are stored to floppy:
lbu include /home/*

Also remeber to move any newly created users to /var/home and create a link:
adduser bob
mv /home/bob /var/home/
ln -s /var/home/bob /home/bob
lbu include /home/bob

Save to floppy:
lbu commit floppy

== Test it works ==
Reboot computer. Now should the raid start and /var sould be mounted. Check with df:
~ $ df
Filesystem 1k-blocks Used Available Use% Mounted on
none 255172 23976 231196 9% /
mdev 100 0 100 0% /dev
/dev/cdrom 140932 140932 0 100% /media/cdrom
/dev/md1 37977060 180984 35866948 1% /var

== Upgrades ==
Since the package database is placed on disk, you cannot update by simply replacing the CDROM. You will have to either run the upgrade on the new CDROM or run ''apk_add -u ... && update-conf'' manually.

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Setting up a /var partition on software IDE raid1