Re: Initrd and software raid [was: Initrd rocks!]

[Eduard Bloch <blade@debian.org>]

#include <hallo.h>
* Florent Rougon [Wed, Dec 10 2003, 09:48:55AM]:

> Note: this starts the root array only; the other arrays are started by a
>       "mdadm -A -s" from /etc/init.d/mdadm-raid.
> 
> > IIRC, There is a parameter to mdadm (--scan?) that could be used for
> > this, but when I asked the initrd maintainer I was given a good reason
> > why it was not used (sorry; I can't remember what this was now; it might
> > simply be that the mdadm code is unreliable, inefficient, or buggy).
> 
> I think this is unlikely, since (-s = --scan) is what is used in the
> Debian aforementioned init script for mdadm (/etc/init.d/mdadm-raid).

That is simply wrong. The mdadm-raid init script uses the mdrun script
which was written IIRC because of following reasons:

 --scan was not reliable under certain circumstance (don't remember the
   details)
 --scan output needed to be stored somewhere which did not work if / got
   corrupted and cannot be mounted readonly or on initrd before tmpfs or
   such are available

So something was needed to emulate the exact behaviour of the kernel
autodetection using a userspace tool, mdrun was born.

Herbert did not accept mdrun for initrd-tools but choosed a "manual"
mode where all used device files are detected and noted in initrd
scripts, then recreated in tmpfs at boot time, using mdadm on them.

MfG,
Eduard.
-- 
Freude beruht auf dem frohen Glauben, daß das Gute überwiegt.