Re: BSD disklabel and autodetection

On Monday July 29, mjt@tls.msk.ru wrote:

martin@hack.org wrote:

quoted

[]

quoted

following some hints i've seen elsewhere on the list i tried to pass md
parameters to the kernel ->

Booting on Nautilus using machine vector Nautilus from SRM
Command line: ro root=/dev/md1 md=1,/dev/sdb5,/dev/sdc2,/dev/sdd2 raid=noautodetect
md: Will configure md1 (super-block) from /dev/sdb5,/dev/sdc2,/dev/sdd2, below.

with the raid=noautodetect option it works.

what other raid/md options can be passed this way? and how do i configure
more than one device? geez, hope there's not a 256 char limit to the
command line...

You may use md=N,dev1,dev2,... option as many times as you want, i.e.

 linux root=... md,1=/dev/sda1,.. md=2,/dev/sda2,...

I think that it's sufficient to tell it about only ONE member of
an array this way if your raid device has persistent superblock
(kernel will read superblock from first disk (or second for that
matter - if you choose to tell it about second disk) and read
other devices from there).

Nope.  You have to list all component devices.  (Storing device
identification in the superblock is a bad idea that doesn't work in
general, but does in enough specific cases that people still seem to
like it).

About other options - there are only two, raid= (e.g. noautodetect)
and md= (above) that are raid-related.

quoted

are these options documented somewhere??

I personally looked at sources in drivers/md/ directory and got the
above line by reading initialization functions.  Maybe it's documented
somewhere in Documentation/... ;)

  Documentation/md.txt

Personally, I am not a big fan of autodetection at all.

I see two reasonable ways to start up the RAID array that
stores the root filesystem.

  1/ kernel parameters like:
                md=0,/dev/sda1,/dev/sdb1

  2/ use an initrd filesystem and a user-mode program that
    finds and assembles arrays based on a simple config file.

All non-root raid arrays should be assembled after boot by
a user-mode program.
I use and recommend mdadm
   http://www.cse.unsw.edu.au/~neilb/source/mdadm/

You can tell it how to recongnise parts of an array and 
it goes hunting, finds them, and assembles the array.

NeilBrown