Installing onto RAID

[bscott at ntisys.com]

On Tue, 17 Sep 2002, at 2:23pm, pll at lanminds.com wrote:
> I want to mirror all the file systems on all 4 drives ...

  AFAIK, this is not supported in the Linux "md" driver.  It should be
pretty easy to do, but it has not been done.

> ... such that if any one drive fails, the system should be able to boot
> from the next bootable device.

  Keep in mind that, if an IDE device fails, it will often hang the entire
IDE bus (or controller (or machine)).

  Anyway, booting from a mirror set is possible, but you need special
support for it.  Red Hat, for example, distributes a patched LILO which
understands a RAID-1 "md" device.  I have no idea how/if GRUB supports RAID.

> In order to mirror across all the drives, don't I need to install to all
> the drives?

  Yes.

> And if so, how do I configure the RAID set *before* I install?

  The same way you do anything before the install -- using the installer.  
If the installer does not support installing to a software RAID, you may be
able to do it manually "behind the scenes" (i.e., on another virtual
console), and then install to the newly created RAID device.  But that
depends largely on your installer.  It would help if we knew what
distribution and release you were planning on using.  :-)

> Or, is there a way to install to the primary master, yet create a
> /etc/raidtab file which then gets read and invoked at boot time and will
> mirror whatever is on /dev/hdaX to /dev/hd[b,c,d]X ?

  You can install to a "failed mirror", i.e., a mirror set with only one
physical device, but you still need to do the RAID setup and install to the
RAID device.

  (Actually, that may not be precisely true.  I believe Linux software RAID
writes the RAID metadata to the end of the physical device.  So, you could,
in theory, create a slightly-smaller partition, install to it, then expand
the partition, create the "failed mirror", and then tell it to re-mirror to
the "other" disk.  But that is so kludgey it makes my skin crawl.)

-- 
Ben Scott <bscott at ntisys.com>
| The opinions expressed in this message are those of the author and do not |
| necessarily represent the views or policy of any other person, entity or  |
| organization.  All information is provided without warranty of any kind.  |