Managing RAID on Linux - Derek Vadala [103]
Most of 3DM's other features are very straightforward, and its documentation is thorough and accessible via the web interface. Use the Configuration tab to perform administrative tasks without taking the system offline. From the Configuration tab, you can add spare disks, remove failed disks, rebuild faulty arrays, and schedule regular integrity checks. The Settings tab controls 3DM's settings, but it also contains options to change the write caching for individual arrays, as well as the amount of the controller's resources dedicated to background tasks such as media verification and array rebuilds. The Monitor and Alarms tabs display status information about the controller and its arrays. And configuration information about the controllers and arrays is provided under the Details tab.
Running 3DM is not a requirement, but it will provide some additional helpful information about your 3ware arrays and controllers. Even if you prefer not to use the web interface to manage and monitor arrays, 3DM still provides useful information via syslog for a more traditional approach.
LSI Logic (MegaRAID)
LSI Logic (http://www.lsilogic.com) sells a variety of SCSI and ATA RAID controllers, all of which are directly supported by Linux. I evaluated both the Elite 1650, a dual-channel SCSI controller, and the MegaRAID i4, a quad-channel ATA controller. Working with these controllers is identical, except for some hard disk-specific configuration options. So the information in this section applies to both the ATA and the SCSI controllers.
Like some of the Adaptec controllers, LSI Logic RAID controllers have also shipped as OEM products with Dell systems. If you have a Dell system with a branded LSI Logic controller, you might want to take a look at Matt Domsch's page on the subject: http://www.domsch.com/linux/.
Creating an Array
Users have two options when creating an array for the first time. When the controller's initialization banner appears, a choice between the MegaRAID Configuration Utility (CTRL-M) and WebBIOS (CTRL-H) is presented. The difference between the two really boils down to ease of use. The MegaRAID Configuration Utility is a typical menu-driven utility, while WebBIOS is a mouse-driven GUI tool. WebBIOS is a bit slower, and since it does require a mouse, it might not be a good choice for some systems, despite its ease of use. On the other hand, the legacy configuration utility is a bit cryptic. Some of its navigation and menus are confusing, and it's sometimes not clear what changes you are making to arrays and disks.
Installing Linux Directly to a MegaRAID Controller
Since support for LSI Logic controllers is integrated into the Linux kernel, distribution support is common and straightforward. Arrays appear during Linux installation as standard SCSI devices, and no special driver disks are needed. I tested installation using Red Hat, SuSE, Mandrake, and Debian.
The MegaRAID Driver
LSI Logic controllers are supported by the megaraid kernel driver, which is found in the SCSI low-level drivers configuration submenu:
SCSI support --->
SCSI low-level drivers --->
...
<*> AMI MegaRAID support
...
There are no other configurable kernel options for the megaraid driver.
Converting an Existing Standalone Disk to a Mirror
Follow these steps if you want to replace your existing disk controller with an LSI Logic RAID controller and mirror your existing system disk.
Before physically replacing the controller, configure a new kernel with support for the megaraid driver. After the kernel is compiled, install it and add an /etc/lilo.conf stanza for it. Don't forget to run /sbin/lilo to rebuild the master boot record, too.
Power down the system and install the new controller in place of your original disk controller. Connect your existing disk and any new disks to the new LSI Logic RAID adapter.
After powering on the system, use CTRL-M to enter the MegaRAID Configuration Utility. (You can, alternatively,