Managing RAID on Linux - Derek Vadala [101]
3ware Escalade ATA RAID Controller
3ware, Inc. sells several well-supported, multichannel ATA RAID controllers. Adam Radford developed an open source driver for 3ware. Joel Jacobson and Brad Strand of 3ware also worked on the driver, as well as Arnaldo Carvalho de Melo of Conectiva, Andre Hedrick of SuSE, and of course, Alan Cox.
The driver supports all 3ware controllers and has been standard in the stable Linux kernel since 2.2.15. Direct installation to 3ware controllers is simple and headache-free. You should have no issues when working with any distribution that uses a 2.4 or later kernel. I enjoyed problem-free installation using Red Hat, SuSE, and Mandrake.
Creating an Array and Installing Linux
The following steps outline the process for creating a new array and installing Linux onto a new system with a 3ware controller. The Kernel Configuration section later in this chapter outlines the process for adding 3ware support to the kernel on an existing system.
When the controller's startup banner appears, press ALT-3 to access the configuration screen. The main menu is split into a list of disks and a list of arrays. No arrays will appear during the first use.
Use the arrow keys to navigate and the ENTER key to select disks for inclusion in the new array. An asterisk appears next to each disk once it has been selected.
After the desired disks are selected, navigate to the Create Array button at the bottom of the screen and press the ENTER key.
An array properties screen appears. Use the arrow and ENTER keys to adjust the RAID level, cache type (write-through or write-back) and stripe size as needed. Select OK when finished, and you'll be returned to the main menu.
Press F8 to commit the new array to the controller's memory. Some additional warnings may appear, indicating that data on the selected disk will be destroyed. Confirm the warnings if you are certain that the disks contain no important data and you want to continue creating the array. If you created an array with redundancy, a synchronization process will start before the system reboots. When the system restarts, the new array appears in the controller's initialization banner.
When you install Linux, the array you created will show up as a standard SCSI device. If you created only one array and have no other disks, the array appears as /dev/sda during installation. Create partitions as you would with any standalone disk and proceed with the installation as you would normally.
Converting an Existing Standalone Disk to a Mirror
I was not able to successfully import a single disk into a 3ware mirror without compromising the existing data. I recommend using a traditional backup and restore procedure if you have a single disk system that you would like to upgrade to a RAID-1 using a 3ware controller.
Kernel Configuration
3ware controllers use the 3w-xxxx SCSI driver. If you installed Linux directly onto a 3ware controller, 3w-xxxx support is already enabled (although it is likely a loadable kernel module). Follow the steps in this section if you are installing a 3ware controller into an existing Linux system or want to compile a kernel without the 3w-xxxx driver as a module. Although I have used the 2.4.18 kernel throughout most of this book, I recommend using a later kernel (2.4.19 became available in August 2002) for this process because the 3ware driver code has been significantly updated. It's likely that the 2.4.19 kernel will not make it into any distributions for quite some time, so I recommend manually upgrading after the initial installation when possible. Readers who are already using a 2.5 development kernel should already have the most recent code.
Support for 3ware ATA RAID controllers is found in the SCSI support section of the Linux kernel.
SCSI support --->
...
SCSI low-level drivers --->
<*> 3ware Hardware ATA-RAID support
...
Enable support statically (as I have shown above) or as a loadable kernel