[gentoo-amd64] Re: SATA mdraid woes

[Duncan]

"Peter Humphrey" <prh@××××××××××.uk> posted
20061228180653.40B4A2B8ADF@×××××××××××××××.uk, excerpted below, on  Thu,
28 Dec 2006 18:06:48 +0000:

[snipped]

> md: linear personality registered for level -1
> md: raid0 personality registered for level 0
> md: raid1 personality registered for level 1
> [so I've got mdraid compiled in]
> ...
> Activating mdev
> Detected real_root as a md device. Setting up the device node
> Determining root device...
> Mounting root...
> ...
> The root block device is unspecified or not detected.
> --
> [end of transcript]
> Then I'm invited to specify another device, or enter a shell. I use the
> shell to say "ls -l /dev/md2", which shows the block device I expect to see,
> but "cat /dev/md2" returns an empty result. If I do that from the
> installation CD I get a dump of the contents of the md disk, so it seems
> that the node exists but it isn't connected to the array /dev/md2.
>
> All I can think of is that I've made an error in creating the RAID-1 arrays,
> but can anyone point me to what that might be?

>From what I've seen, there aren't a lot of folks on this list doing RAID,
and some of the ones that are, are using the DM-RAID firmware-RAID stuff,
rather than md-RAID.

I'm doing RAID, but RAID-only, no non-RAID boot and no initramfs, so that
aspect of it I'm unfamiliar with and that seems to be the problem, so I'll
be of limited help.  I'm /guessing/ the most likely list to have real RAID
experts on it is going to be the gentoo-server list, which I've never
subscribed to so I can't say for sure /what/ they call topical there.

FWIW tho I don't see that it's going to help you presently, unless you
decide to rework to do something similar, I'm setup using md RAID-0, -1,
and -6 on four identically partitioned SATA drives. RAID-0 for /boot since
GRUB can work with it.  Partitioned RAID-6 for my main system, with root
(including everything portage writes to, so much of /var and /usr, on
root, keeping portage in sync with what's on the partition) and a backup
root image on two of the RAID-6 partitions (I'd go with a second backup
image if I redid it) and an LVM2 managed RAID-6 partition as well for
data.  The RAID-0 covers all the temp and redownloadable stuff such as the
portage tree.

Critically, my root and backup root partitions are directly on the
partitioned RAID-6, not on LVM2, so I don't need an initramfs.  md-RAID is
built-in and can be configured on the kernel command line from GRUB, while
LVM2 requires userspace configuration, thus an initramfs, which I can
avoid by placing my root and backup directly on partitioned RAID-6
partitions.

Thus, in the event of motherboard/SATA-chipset hardware failure, all
that's needed to get going again is a new mobo and the ability to compile
a kernel with the appropriate standard SATA drivers for the new chipset. 
The kernel is pointed at the correct root from its command line directly,
no initramfs or the like needed, and lvm2 loads from the main root and
only manages non-system data, so I have a fully working root complete with
all the usual binaries to work with if I have lvm2 issues.

-- 
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

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