16.4 RAID

16.4.1.1.1 Installing the Hardware

In addition to the IDE system disk, three Western Digital 30GB, 5400 RPM IDE disks form the core of the CCD disk described below providing approximately 90GB of online storage. Ideally, each IDE disk would have its own IDE controller and cable, but to minimize cost, additional IDE controllers were not used. Instead the disks were configured with jumpers so that each IDE controller has one master, and one slave.

Upon reboot, the system BIOS was configured to automatically detect the disks attached. More importantly, FreeBSD detected them on reboot:

ad0: 19574MB <WDC WD205BA> [39770/16/63] at ata0-master UDMA33
ad1: 29333MB <WDC WD307AA> [59598/16/63] at ata0-slave UDMA33
ad2: 29333MB <WDC WD307AA> [59598/16/63] at ata1-master UDMA33
ad3: 29333MB <WDC WD307AA> [59598/16/63] at ata1-slave UDMA33

Next, consider how to attach them as part of the file system. You should research both vinum(8) (Chapter 17) and ccd(4). In this particular configuration, ccd(4) was chosen.

16.4.1.1.2 Setting Up the CCD

The ccd(4) driver allows you to take several identical disks and concatenate them into one logical file system. In order to use ccd(4), you need a kernel with ccd(4) support built in. Add this line to your kernel configuration file, rebuild, and reinstall the kernel:

pseudo-device   ccd     4

On 5.X systems, you have to use instead the following line:

device   ccd

The ccd(4) support can also be loaded as a kernel loadable module in FreeBSD 3.0 or later.

To set up ccd(4), you must first use disklabel(8) to label the disks:

disklabel -r -w ad1 auto
disklabel -r -w ad2 auto
disklabel -r -w ad3 auto

This creates a disklabel for ad1c, ad2c and ad3c that spans the entire disk.

The next step is to change the disk label type. You can use disklabel(8) to edit the disks:

disklabel -e ad1
disklabel -e ad2
disklabel -e ad3

This opens up the current disk label on each disk with the editor specified by the EDITOR environment variable, typically vi(1).

An unmodified disk label will look something like this:

8 partitions:
#        size   offset    fstype   [fsize bsize bps/cpg]
  c: 60074784        0    unused        0     0     0   # (Cyl.    0 - 59597)

Add a new e partition for ccd(4) to use. This can usually be copied from the c partition, but the fstype must be 4.2BSD. The disk label should now look something like this:

8 partitions:
#        size   offset    fstype   [fsize bsize bps/cpg]
  c: 60074784        0    unused        0     0     0   # (Cyl.    0 - 59597)
  e: 60074784        0    4.2BSD        0     0     0   # (Cyl.    0 - 59597)

16.4.1.1.3 Building the File System

The device node for ccd0c may not exist yet, so to create it, perform the following commands:

cd /dev
sh MAKEDEV ccd0

Now that you have all the disks labeled, you must build the ccd(4). To do that, use ccdconfig(8), with options similar to the following:

ccdconfig ccd0 32 0 /dev/ad1e /dev/ad2e /dev/ad3e

The use and meaning of each option is shown below:

After running ccdconfig(8) the ccd(4) is configured. A file system can be installed. Refer to newfs(8) for options, or simply run:

newfs /dev/ccd0c

16.4.1.1.4 Making it All Automatic

Generally, you will want to mount the ccd(4) upon each reboot. To do this, you must configure it first. Write out your current configuration to /etc/ccd.conf using the following command:

ccdconfig -g > /etc/ccd.conf

During reboot, the script /etc/rc runs ccdconfig -C if /etc/ccd.conf exists. This automatically configures the ccd(4) so it can be mounted.

To automatically mount the ccd(4), place an entry for the ccd(4) in /etc/fstab so it will be mounted at boot time:

/dev/ccd0c              /media       ufs     rw      2       2