RAID1 root - troubles booting in degraded mode

RAID1 root - troubles booting in degraded mode

[Massimiliano Masserelli]

Hi folks! 

I've taken a look at the ML archives, and found an old thread (06/2002) 
on this subject, but found no solution.

I've a working setup with a two disks RAID1 root, which boots
flawlessly. Troubles arise when simulating hw failure. RAID setup is as
follows:

raiddev                 /dev/md0
raid-level              1
nr-raid-disks           2
nr-spare-disks          0
chunk-size              4

device                  /dev/hda1
raid-disk               0

device                  /dev/hdc1
raid-disk               1

If I disconnect /dev/hda before booting, the kernel tries to initialize
the array, can't access /dev/hda1 (no wonder), marks it as faulty, then
refuses to initialize the array, dieing with a kernel panic, unable to
mount root.

If I disconnect /dev/hdc before booting, the array gets started in
degraded mode, and the startup goes on without a glitch.

If I disconnect /dev/hda and move /dev/hdc to its place (so it's now
/dev/hda), the array gets started in degraded mode and the startup goes
on.

Actually, this is already a workable solution (if the first disk dies, I
just "promote" the second to hda and go looking for a replacement of the
broken disk), but I think this is not _elegant_. 8)

Could anyone help me shedding some light on the subject?

Tnx in advance.
-- 
Massimiliano Masserelli
-------------------------------------------------------------------------------
Mayor: "Uh... try to have her home by eleven."
	--Buffy the Vampire Slayer: Enemies

Re: RAID1 root - troubles booting in degraded mode

[Massimiliano Masserelli]

On Wed, Oct 30, 2002 at 11:52:25AM +0100, Martin Bene wrote:

> This look like you're initializing the array from an initrd using
> raidstart.

Indeed I am.

> Reason why it's not working: raidstart is stupid. it just reads the
> first device from raidtab and tries to read the raid superblock from
> there. if the first device listed in raidtab doesn't work, raidstart
> can't start the array.

Pity I didn't find this little detail in any of the docu I found and
read... Thank you very very much for the hint, I'll make some
experiments (static raid support vs. mdadm).

Bye.
-- 
Massimiliano Masserelli
-------------------------------------------------------------------------------
Nella sua prima passione la donna ama il suo amante,
in tutte le altre cio` che ama e` il suo amore.
    	-- Byron, "Don Juan"

Re: RAID1 root - troubles booting in degraded mode

[Emilio Gargiulo]

Hi Massimiliano
Have you tryed to set partition id to 0xFD <raid autodetect>, and use a boot 
string as:
root=/dev/md1 ro devfs=mount vga=791
I have the same configuration, and I have a grub bootloader on each raid disk.

Emilio Gargiulo

Alle 00:07, mercoledì 30 ottobre 2002, Massimiliano Masserelli ha scritto:
> Hi folks!
>
> I've taken a look at the ML archives, and found an old thread (06/2002)
> on this subject, but found no solution.
>
> I've a working setup with a two disks RAID1 root, which boots
> flawlessly. Troubles arise when simulating hw failure. RAID setup is as
> follows:
>
> raiddev                 /dev/md0
> raid-level              1
> nr-raid-disks           2
> nr-spare-disks          0
> chunk-size              4
>
> device                  /dev/hda1
> raid-disk               0
>
> device                  /dev/hdc1
> raid-disk               1
>
> If I disconnect /dev/hda before booting, the kernel tries to initialize
> the array, can't access /dev/hda1 (no wonder), marks it as faulty, then
> refuses to initialize the array, dieing with a kernel panic, unable to
> mount root.
>
> If I disconnect /dev/hdc before booting, the array gets started in
> degraded mode, and the startup goes on without a glitch.
>
> If I disconnect /dev/hda and move /dev/hdc to its place (so it's now
> /dev/hda), the array gets started in degraded mode and the startup goes
> on.
>
> Actually, this is already a workable solution (if the first disk dies, I
> just "promote" the second to hda and go looking for a replacement of the
> broken disk), but I think this is not _elegant_. 8)
>
> Could anyone help me shedding some light on the subject?
>
> Tnx in advance.

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Re: RAID1 root - troubles booting in degraded mode

[Massimiliano Masserelli]

On Wed, Oct 30, 2002 at 09:18:13PM +0100, Emilio Gargiulo wrote:

> Have you tryed to set partition id to 0xFD <raid autodetect>, and use
> a boot string as: root=/dev/md1 ro devfs=mount vga=791

Yes, I tried, but to no avail. Creating an initrd image with mdadm in
the startup script solved the issue.

Bye.
-- 
Massimiliano Masserelli
-------------------------------------------------------------------------------
L'importante e` di non fare di tutta la merda un fascio.
                -- Altan