[gentoo-amd64] Re: How to install to a RAID set?

[Duncan]

Nuitari posted <Pine.LNX.4.64.0605061613320.2752@××××××××××××××××.net>,
excerpted below,  on Sat, 06 May 2006 16:18:05 -0400:

> After quite a few experience with most software RAID that require drivers
> I have come to the conclusion that they are not worth anything. You are
> much better off using Linux software raid which will work even if you
> change chipsets, as in upgrading your computer in a later point in time.
> Also there are quite a few software Raid out there that require you to
> rebuild the Raid if you ever update the Bios.

That has been my conclusion as well.  I'm /extremely/ happy with my
quad-SATA Linux kernel based RAID setup.  One of the benefits is that one
doesn't have to choose a single RAID type for the entire disk set.  I'm
also counting on the fact that I can switch the SATA controller to
any chipset I want at any time, or upgrade BIOS, or anything else, without
having to rebuild the raid.

The layout here:

* A small RAID-1 for /boot.  Set up correctly, one can boot from any of
the drives in the RAID-1.  I have four drives, and I can set the BIOS to
boot from any of the four.

* A large partitioned RAID-6, for two-way redundancy, yet it's still
two-way striped as well.  The first partition is root (incl. /usr and
/var, thereby keeping the portage database in sync with what's actually on
the partitions), the second rootbak, a snapshot of root copied off
periodically, allowing me to boot to it in the event the main root won't
boot, for some reason.  I can also boot to it for recovery if portage
breaks on my main root.  It's identically sized to root, and likewise
includes its own synced /usr and /var/db/portage, tho of course root and
rootbak aren't in sync with each other except at the moment I've just
finished a backup snapshot.

Note the choice of partitioned RAID, rather than LVM, for root and
rootbak.  That's deliberate, as Linux kernel RAID is just that --
in-kernel, while LVM requires some userland help.  That means if I used
LVM for root, I'd have to hassle an initramfs (formerly initrd), something
I can avoid by putting root (and rootbak) on partitioned RAID.  The kernel
is loaded by GRUB from any of the /boot RAID-1 images, and the kernel is
all that's required to load /root, as it has everything built-in that  it
would need.

* A third partition on that RAID-6, bigger than the root and rootbak
partitions, used with LVM.  The LVM logical volumes on this partition
contain /home and homebak, /usr/local and a backup, /var/log with no
backup, mail and news partitions with a backup for mail, not news, my
media partition and its backup, the  portage packages dir (I use
FEATURES=buildpkg) and its backup, etc.

* A partitioned RAID-0 with two partitions, /tmp on one, and a second
partition containing the portage tree, the ccache cache, and the kernel
tree (symlinked from /usr/src), each in its own subdir.  Note that all of
these benefit very highly from the RAID-0, while not needing any
redundancy as they are easily redownloaded or rebuild.

With this setup, I have about the best mix possible, easy booting with no
serious complications, redundancy both in RAID and in snapshot backup
where I need it, and no hardware lockin -- I can replace two of the four
drives at once without losing anything but the throw-away data on the
RAID-0, and can switch out SATA chipsets and/or motherboard without losing
anything, either.  It's a combination no hardware RAID could ever match.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman in
http://www.linuxdevcenter.com/pub/a/linux/2004/12/22/rms_interview.html


-- 
gentoo-amd64@g.o mailing list