12.4 RAID

12.4.1.1.1 Installing the Hardware

I installed the hard drives in a system that already had one IDE disk in as the system disk. The ideal solution would be for each IDE disk to have its own IDE controller and cable, but without fronting more costs to acquire a dual IDE controller this would not be a possibility. So, I jumpered two disks as slaves, and one as master. One went on the first IDE controller as a slave to the system disk, and the other two where slave/master on the secondary IDE controller.

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

At this point, if FreeBSD does not detect the disks, be sure that you have jumpered them correctly. I have heard numerous reports with problems using cable select instead of true slave/master configuration.

The next consideration was how to attach them as part of the file system. I did a little research on vinum(8) (Chapter 13) and ccd(4). In this particular configuration, ccd(4) appeared to be a better choice mainly because it has fewer parts. Less parts tends to indicate less chance of breakage. Vinum appears to be a bit of an overkill for my needs.

12.4.1.1.2 Setting up the CCD

CCD allows me to take several identical disks and concatenate them into one logical file system. In order to use ccd, I need a kernel with ccd support built into it. I added this line to my kernel configuration file and rebuilt the kernel:

    pseudo-device   ccd     4

ccd support can also be loaded as a kernel loadable module in FreeBSD 4.0 or later.

To set up ccd, first I need to disklabel the disks. Here is how I disklabeled them:

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

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

The next step is to change the disklabel type. To do that I had to edit the disklabel:

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

This opened up the current disklabel on each disk respectively in whatever editor the EDITOR environment variable was set to, in my case, vi(1). Inside the editor I had a section like this:

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

I needed to add a new "e" partition for ccd(4) to use. This usually can be copied of the "c" partition, but the fstype must be 4.2BSD. Once I was done, my disklabel should look 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)

12.4.1.1.3 Building the File System

Now that I have all of the disks labeled, I needed to build the ccd. To do that, I used a utility called ccdconfig(8). ccdconfig takes several arguments, the first argument being the device to configure, in this case, /dev/ccd0c. The device node for ccd0c may not exist yet, so to create it, perform the following commands:

    cd /dev
    sh MAKEDEV ccd0

The next argument ccdconfig expects is the interleave for the file system. The interleave defines the size of a stripe in disk blocks, normally five hundred and twelve bytes. So, an interleave of thirty-two would be sixteen thousand three hundred and eighty-four bytes.

After the interleave comes the flags for ccdconfig. If you want to enable drive mirroring, you can specify a flag here. In this configuration, I am not mirroring the ccd, so I left it as zero.

The final arguments to ccdconfig are the devices to place into the array. Putting it all together I get this command:

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

This configures the ccd. I can now newfs(8) the file system.

    newfs /dev/ccd0c

12.4.1.1.4 Making it all Automatic

Finally, if I want to be able to mount the ccd, I need to configure it first. I write out my current configuration to /etc/ccd.conf using the following command:

    ccdconfig -g > /etc/ccd.conf

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

If you are booting into single user mode, before you can mount the ccd, you need to issue the following command to configure the array:

    ccdconfig -C

Then, we need an entry for the ccd in /etc/fstab so it will be mounted at boot time.

    /dev/ccd0c              /media       ufs     rw      2       2