17.4 RAID

17.4.1.1.1 安裝硬體

除了系統磁碟外，下面介紹的 CCD 磁碟陣列將使用到三顆 30GB、 5400 RPM 的 Western Digital IDE 磁碟，以提供約 90GB 的儲存空間。 最理想的情況是每個磁碟由獨立使用的排線連接獨立使用的 IDE 控制器， 不過為了降低成本，利用 jumper 設定磁碟，使每個 IDE 控制器可連接 一個主磁碟加一個副磁碟，如此可不必加裝額外的 IDE 控制器。

開機後，BIOS 應該設定成自重偵測磁碟。更重要的是 FreeBSD 應該 要偵測到它們：

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

接下來，考慮如何將它們變成檔案系統的一部份。您可以參考 vinum(8)(Chapter 19) 及 ccd(4)。 在此我們選擇 ccd(4) 。

17.4.1.1.2 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:

device   ccd

The ccd(4) support can also be loaded as a kernel loadable module.

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

bsdlabel -r -w ad1 auto
bsdlabel -r -w ad2 auto
bsdlabel -r -w ad3 auto

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

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

bsdlabel -e ad1
bsdlabel -e ad2
bsdlabel -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)

17.4.1.1.3 Building the File System

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

17.4.1.1.4 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