Managing RAID on Linux - Derek Vadala [86]
Configuring the kernel
The DAC960/DAC1100 driver is located under the Block Devices submenu (see Figure 5-1) and can be compiled statically or as a loadable kernel module.
Figure 5-1. Enable the DAC960/DAC1100 driver for Mylex support.
Once you have enabled support for the DAC960/DAC1100 driver, you can rebuild and install the new kernel, using the make dep and make bzImage commands.
Device special files
The DAC960/DAC1100 uses a Devfs-style naming system. All device files are located in the /dev/rd directory and are named to reflect the controller, logical device, and partition numbers. For example, /dev/rd/c0d0p1 refers to first partition (p1) of controller zero's (c0) first logical drive (d0). In general, /dev/rd/cXdYpZ refers to controller X, logical drive Y, and partition Z. This naming method is useful because unlike standard SCSI devices, disks do not change names when a disk fails.
Partition limitations
All Mylex arrays and logical drives are limited to seven partitions. This limit can be constraining when you're working with a single large array and also using a standard FHS partitioning scheme.
For example, let's say that you have a 100 GB RAID-5 that you are using for both system and data disks. The seven-partition limit constricts standard filesystem segmentation, because after allocating a separate partition for /boot, /, /home, /usr, /tmp, /var, and swap, you've hit the partition limit. You can't even add separate /usr/local and /opt partitions when necessary. And the seven-partition limit certainly doesn't leave any room for creating new partitions for databases, network filesystems, or web servers.
In cases such as this, it's useful to simply split a large array into multiple logical drives. You can allocate a couple of small logical drives for system partitions and leave the remaining space on a separate logical drive to partition as needed for larger data filesystems.
Controller Setup
After installing a Mylex RAID controller, you should see a message similar to the following when you power on the system:
Scanning Option ROMs...
Mylex AcceleRAID 352 BIOS PLUS V6.01-30 (Nov 14, 2001)
Copyright (c) 2001 IBM Corporation. All rights reserved.
www.mylex.com
Spinning up drives......
AcceleRAID 352 Firmware Version 7.00-03
RAID Adapter Serial #: 10026500327
PCI Address: F0000000 Bus=2 Dev/Slot=13 Function=0 IRQ=9
Adapter Memory Size = 64 MB (SDRAM/ECC)
BIOS Enabled - 8 GB Disk Drive Geometry Selected.
Press Press No system drives installed If arrays had already been defined, the last line would have displayed the number of arrays (logical drives) in the controller's configuration. The banner also displays the amount of memory installed in the controller, the firmware version, and the card's PCI address, location, and interrupt. BIOS options Press ALT-M to enter the BIOS options menu. There are three options, each of which controls the card's ability to boot the system. BIOS enabled/disabled The BIOS must be enabled if you wish to boot from disks, arrays, or CD-ROM drives connected to the controller. If you don't want to boot from these devices, you can disable the BIOS and shave a few seconds off the system startup. The remaining options do not apply if this option is disabled. CD-ROM boot enabled/disabled If you want to boot from a CD-ROM drive that is connected to your Mylex controller, this option must be enabled. Remember that using a slower device (such as a CD-ROM) on a fast SCSI channel will cause the entire channel to run at the speed of the slowest device. You probably don't want to connect a CD-ROM to an expensive RAID controller. However, this option is quite useful for system installation. Disable it when you're done using the CD-ROM, and don't forget to disconnect the drive. 2 GB/8 GB drive geometry This option selects how much of an array/disk the BIOS can address. When set to 2 GB, the controller