Re: 16 HDDs too much for RAID6?

["Lars Täuber" <taeuber@bbaw.de>]

Hi guys,

Luca Berra <bluca@comedia.it> schrieb:
> On Thu, Mar 06, 2008 at 05:16:21PM +0100, Andre Noll wrote:
> >On 11:55, Lars Täuber wrote:
> >> monosan:~ # cat /etc/mdadm.conf 
> >> DEVICE partitions
> >> ARRAY /dev/md2 level=raid1 UUID=d9d31de2:e6dbd3c3:37c7ea09:882a64e5
> >> ARRAY /dev/md3 level=raid1 UUID=a8687183:a79e514c:ca492c4b:ffd4384f
> >> ARRAY /dev/md4 level=raid6 num-devices=16 UUID=8d596319:4d21dba3:3871bccf:5b90a66d
> >
> >Does it help to list only the 16 devices that are used for the array,
> >i.e. something like
> >
> >	DEVICE /dev/sd[a-p]

because the devices sd[c-z] and sda[a-h] are used by multipathd they are accessible in read only mode only. For writing /dev/dm-* devices are available.

> i hope kernel will pevent you from doing something this stupid, but i am
> not that sure.
> if you wanna check if the problem is device selection a more appropriate
> line would be
> DEVICE /dev/mapper/mpath*
> or
> DEVICE /dev/dm-[0-9] /dev/dm-1[0-5]

Correct.
My mdadm.conf has now this line for safety:
DEVICE /dev/sd[ab][0-9] /dev/dm-*

But this doesn't really changed anything.

> >I think this is what is confusing mdadm. Your "DEVICE partitions"
> >line instructs mdadm to consider all devices in /proc/partitions,
> >so it finds both sdy and sdi.
> in this case i believe the error message would be different
> 
> >> Is there a way to get more verbose infos or debug this anyhow?
> 
> you could try with the --verbose option and post the results here.
> 
> also could you check if the minor number of /dev/dm-* are really unique?
> 
> in case this yelds no result we will have to add some more printf in
> Assemble.c.

I zeroed out all physical devices completely:
# for DEV in /dev/sd[c-r]; do dd if=/dev/zero of=$DEV; done

Now the problem is gone. I don't know what really caused the problem.
Many thanks for your suggestions.

Lars
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