High Availability Linux with Software RAID

Once the drives are partitioned in this way, I can create the RAID 5 volumes. Table 2 shows the RAID volume configuration.

Because of parity, each RAID volume of five partitions has a size of four times the partition size. Table 3 shows my final partition table.

The filesystem type used for the volumes is EXT2. By default, though, Red Hat 8.0 wants to create EXT3 journaling filesystems. At this time, the combination of a journaling filesystem and software RAID makes for very poor performance. There is a lot of talk about working on these performance issues, but for now, EXT2 is the way to go.

During the Red Hat 8.0 install, I used Disk Druid to set up the partitions as outlined above and illustrated in Figures 2 and 3. I used the GRUB boot loader and installed the boot image on /dev/sda. For testing purposes, I installed only about 500MB worth of packages on the VM.

Figure 2. Partitioning with Disk Druid

Figure 3. Setting Up the RAID Device

After the installation has completed, inspection of the files /etc/fstab and /etc/raidtab reflects the partitioning scheme and RAID configuration outlined above.

Executing cat /proc/mdstat as root displays information about the RAID configuration. Here is sample output:

Personalities : [raid5]
read_ahead 1024 sectors
md0 :   active raid5 sdf1[4] sde1[3] sdd1[2] sdc1[1] sdb1[0]
        1027584 blocks level 5, 64k chunk, algorithm 0 [5/5] [UUUUU]
md1:    active raid5 sdf2[5] sde2[4] sdd2[3] sdc2[2] sdb2[1] sda2[0]
        44780800 blocks level5, 64k chunk, algorithm 0 [6/6] [UUUUUU]

This output shows us each of the partitions participating in the RAID volumes and its status. The last two columns in the second line displays important information for each RAID volume. Specifically, it shows the the total drives and active drives (for example, [5/5]) and the status of each drive (U for up? The documentation is unclear).

Using this configuration, if any one of the drives from /dev/sdb through /dev/sdf fails, both RAID volumes /dev/md0 and /dev/md1 would be running in degraded mode but without any data loss. If the /dev/sda drive fails, the RAID volume /dev/md1 would be running in degraded mode without any data loss. In this scenario, however, our /boot partition and the master boot record on /dev/sda would be lost. This is where the creation of a bootable recovery CD comes in.