Root Drive Mirroring and LVM.

Sven Luther sven.luther at
Wed Jan 28 19:15:23 EST 2004

On Wed, Jan 28, 2004 at 12:42:18PM +1100, Neil Brown wrote:
> On Tuesday January 27, atossava at wrote:
> > Sorry about the crossposting.
> >
> > I wrote on the Yellow Dog Linux list when somebody asked about software
> > RAID on YDL about my experiences with it:
> >
> > >> The one really big gotcha is that the Macintosh partitioning scheme
> > >> can't tell the Linux kernel that certain partitions are to be
> > >> considered "Linux RAID autodetect" (as in x86 using the DOS partition
> > >> table type 0xfd). This means that you can't boot a Mac Linux system
> > >> directly from RAID because the kernel won't be able to autostart the
> > >> RAID devices. You have to work around this by creating an initial RAM
> > >> disk that uses the raidstart command to start your metadevices, then
> > >> swaps the initrd out of the way and proceeds to start the real system.
> >
> This is not entirely true.  Certainly an initial-ram-disk is one
> solution and is (I think) the preferred long-term solution. However
> you can also boot from raid with kernel-parameters like:
>    md=0,/dev/hda1,/dev/hdc1 boot=/dev/md0
> where '0' indicated which md device (md0 in this case), and the
> remaining words are the devices to assemble it from.

This is said to be broken on latest 2.4.x kernels though. Didn't try
myself though, since i only have a single drive, and don't really want
to mess up with it.

> > to which Tim Seufert replied on the same list:
> >
> > > Hmmm.  That would seem to be a lack in the Linux RAID code, since the
> > > Macintosh partition table has a vastly more flexible partition type
> > > field than DOS: instead of a single byte it's a string.  It would mean
> > > breaking from the convention of using the "Apple_SVR2_UNIX" type for
> > > Linux partitions, but that really is just a convention as far as I know.
> >
> > Perhaps the PPC Linux developers and the Linux RAID developers should
> > get together on this and make some decisions so as to make it happen.
> >
> I personally think auto-detect is the wrong approach and have no
> desire to extend it to other partition types (I cannot remove it from
> DOS partitions as that breaks back-compatability).
> Just use "md=..."



Sven Luther

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