[CoLoCo] SATA RAID controller

[Kevin Fries]

On Tue, 2008-03-04 at 12:43 -0700, David L. Willson wrote:
> > Jim and I both participate in a mail group that discussed this exact
> > issue about a month ago
Public: Ubuntu Developers

The problem mostly occurs when a RAID-5 needs a rebuild.  Under many
circumstances, the system will not boot.  Ubuntu can not rebuild the
missing information during the boot sequence.  I have never seen a
version of Linux or Windows that can.

Mirrors are a bit different.  Once you get the mirror working, you have
to remember to manually move the boot info to the mirroring disk,
otherwise, a failure of the primary disk will cause the mirror to fail
(unbootable disk, md does not handle this for you automatically).

Booting from software RAID is not for the faint at heart.  It actually
creates a circular logic: you need the drive to boot to resolve issues
on the non-booting drive.  Stripes and Parity create the biggest issues,
mirrors are better because you in theory have a copy of the drive, so as
long as you remember to make that backup disk bootable, you _should_ be
ok.

Hardware RAID hides all these issues behind the ROM on the card, and the
controller's api.

-- 
Kevin Fries
Senior Linux Engineer
Computer and Communications Technology, Inc
A Division of Japan Communications Inc.