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

AW: RAID1 root - troubles booting in degraded mode

[Martin Bene]

Hi Massimiliano

> 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.

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

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.

What to do about it:

a) you could compile raid into your kernel (not as modules), set the
partition type of the raid partitions to 0xfd and have the kernel
automatically initialize the raid array. This works even if device name and
or device order of the raid devices has changed.

or 

b) use Neil Browns mdadm instead of raidstart in the initrd - it's a
replacement for the older raidtools and doesn't have any problem when the
first device is down.

Bye, Martin

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