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List:       linux-raid
Subject:    Re: Raid-5 autodetection problem
From:       Neil Brown <neilb () cse ! unsw ! edu ! au>
Date:       2002-03-31 21:52:51
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On  March 31, steven.rodenburg@planet.nl wrote:
> Subject : Raid-5 autodetection problem
> OS      : Suse 7.3 for Sparc64
> Kernel  : 2.4.19-pre4
> Hardware: Sun Ultra10 512MB RAM, 1x 20GB SUN Ide HD (/dev/hda), 3 x
>           scsi-HD in software RAID-5 config (/dev/md0 and /dev/md1)
>           attached to a Tekram DC390U2B Ultra2 controller.
> Severity: I need a drink...
> 
> 
> Hello, 
> 
> I have a problem with my SUN Ultra10 machine.
> I have 3 scsi-disc's connected to a Tekram scsi-controller (sym53c8xx
> driver) 
> i boot from the onboard IDE disk /dev/hda 
> 
> The scsi-disc's are all part of a perfectly working Raid-5 array 
> i copied the contents of the IDE disk to /dev/md0 
> i modified the, to the array copied, /etc/fstab to say that  /  sits on
> /dev/md0 
> 
> All drivers are built in to the kernel 
> Made a new SILO entry with root=/dev/md0  so i can switch from booting
> with root on the IDE disc and on the Raid5 array. 
> 
> The problem is that the array is detected but not in time (too late) 

Raid Auto-detect only works for ms-dos style partition tables.  You
probably aren't using those partition tables on a Sparc...
The detection that *is* working is probably an init.d script running
raidstart. 

But you don't really need autodetect.
Simply add
    md=0,/dev/sda1,/dev/sdb1,/dev/sdc1

to your SILO boot line and it should work fine.

> 
> Oh, by the way. Does anyone know why the kernel switches raid5 cache
> buffer size like that ? 

The stripe cache size must match the size of requests that are being
received by the raid5 driver.  When the request size changes the cache
is flushed and rebuilt.  Once a filesystem is successfully mounted the
request size stabilises.

NeilBrown
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