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Old 05-07-2010, 04:34 PM
Marius Gedminas
 
Default usb raid1 pendrive boot

On Fri, May 07, 2010 at 01:21:09PM +0200, Jozsi Vadkan wrote:
> Did anyone managed to boot from RAID1?

Yes.

> Lenny gives this error message:
>
> "mdadm: no devices found for /dev/md0"

This is an Ubuntu list; chances are you'll get better support for Lenny
if you ask on a Debian list.

> I just want to install Debian Lenny on two pendrives [in sRAID1], so
> that the HDD's in the pc can be used only as ""data containers"", but it
> gives this error message.

I've been booting from Software RAID-1 partitions in both Ubuntu and
Debian; things generally just work for me.

Is your /etc/mdadm/mdadm.conf correct? Does your initramfs image
contain support for RAID-1?

Marius Gedminas
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Old 05-07-2010, 05:03 PM
Andrew Reid
 
Default usb raid1 pendrive boot

On Friday 07 May 2010 08:22:00 deloptes wrote:
> Jozsi Vadkan wrote:
> > Did anyone managed to boot from RAID1?
> >
> > Lenny gives this error message:
> >
> > "mdadm: no devices found for /dev/md0"
> >

> You'll need a small i.e. 20-30MB partition out of raid to boot from with
> i.e. initrd which loads the md driver and your raid device becomes visible.

* Just for the record, it actually *is* possible to boot off a partition
that's in RAID1, but you might have to use grub. *The reason it works
is because grub can read past the md-raid1 metadata without getting
confused -- since the raid is not running when grub is looking at the
disks, it only sees one of the two, but since they're mirrored, and
since grub doesn't *write* to the partition, everything works.

* I have several production systems that do this.

* It's a bit complicated to set up, but generally, it goes
something like:

* - Install a basic system onto one drive, with the correct
* * * size of partition (call this /dev/sda1).
* - Set up an "incomplete" RAID1 array, with one device and
* * * one missing, with the second drive -- this is /dev/md0,
* * * consisting of /dev/sdb1 and an empty slot.
* - Configure /etc/mdadm/mdadm.conf, and re-build your initramfs
* * * so that it has the md modules and knows about the array.
* - Mount /dev/md0 somewhere and copy all the data off /dev/sda1 to it.
* * * It's very important to get the *new* initramfs onto the array.
* - Install grub in the bootloader of the 2nd drive. (The installer
* * * already did this for the first one). This actually isn't
* * * essential, but you may need it if/when /dev/sda fails.
* - Boot on to the incomplete RAID array -- root=/dev/md0.
* - Add /dev/sda1 to the array, and sync.

* Now you have a bootable software raid-1 system.

* I'm not saying this solves the OP's problem, necessarily,
but it's perfectly possible. *I've never tried it with LILO
or grub2, but I would think it would work.

********************************-- A.
--
Andrew Reid / reidac@bellatlantic.net


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Old 05-07-2010, 09:39 PM
martin f krafft
 
Default usb raid1 pendrive boot

also sprach Andrew Reid <reidac@bellatlantic.net> [2010.05.07.1903 +0200]:
> * Just for the record, it actually *is* possible to boot off a partition
> that's in RAID1, but you might have to use grub. *The reason it works
> is because grub can read past the md-raid1 metadata without getting
> confused

Correction: the md metadata comes after the filesystem. That's why
Grub1 doesn't see it.

Grub2 (grub-pc) can interpret md arrays and is the preferred method.

--
.'`. martin f. krafft <madduck@d.o> Related projects:
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