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From: Andrew Reid on 7 May 2010 13:10
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(a)bellatlantic.net


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