Software RAID issues (was Re: Suggestions solicited, server bring up)

[Ben Scott]

On Wed, Nov 18, 2009 at 1:07 PM, Alan Johnson <alan at datdec.com> wrote:
> The only reason I've ever had to install a driver
> for a RAID controller is for online management.  As far as drive access, all
> the controllers I've come across just look like any other SATA or SCSI
> controller from a device exposure.

  There is no standard software/hardware interface for SATA or SCSI
controllers.[1]

  Some of Intel's ATA chipsets come close -- they're widely emulated
and might qualify as a de facto standard -- but even Intel changes
their stuff now and again.  That's why Win XP needs drivers for many
SATA chipsets -- they don't look like the venerable PIIX IDE
controller anymore.

  Looking at a CentOS 5.x box I have near to hand (kernel package
2.6.18-164.6.1.el5), the kernel has roughly 55 different SATA/SCSI
drivers available.  There are at least three for Adaptec chipsets
alone (aic7xxx, aic7xxx_old, aic94xx).

  I'm not sure exactly what you mean when you say you've never needed
to install a driver, but your Linux computer is certainly loading a
driver for your disk controller, regardless of whether you've got a
RAID controller or just a plain old disk controller.

  If you mean your preferred Linux distro came with the driver
built-in, well, that's good, but there's still a driver being loaded,
and if that driver is buggy you'll still be having a bad time[2].

  If you mean your preferred RAID controller emulates some other
interface, that's also valid, but Linux will still needs a driver for
that other interface.  For example, I've seen gizmos with three IDE
connectors.  You connect a disk each to two of those connectors.  You
connect the third to the motherboard's IDE connector.  The card makes
the two IDE disks look like one to the motherboard.  So Linux does not
need to know about that RAID card -- but it still needs a driver for
the motherboard's IDE controller.

[1] Well, unless you count BIOS INT13, but Linux can't use the
real-mode BIOS, and even MS-DOS systems generally loaded supplementary
drivers because INT13 sucks so much.

[2] Myself, I've never had a problem the "megaraid" driver that's been
part of the standard Linux kernel since circa 2001.  Obviously,
experiences vary.

-- Ben