From mboxrd@z Thu Jan  1 00:00:00 1970
From: Erik =?utf-8?b?SGplbG3DpXM=?= <erik.hjelmas@gmail.com>
Subject: Re: cannot attach backing device, wipefs does not fix it
Date: Wed, 18 Jun 2014 17:11:22 +0000 (UTC)
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References: <loom.20140618T173307-560@post.gmane.org> <1297031660.20140618230148@pvgoran.name>
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> > Hi, ubuntu 14.04, and a 5TB RAID (sdc) partitioned into two 2.5TB partitions
> > (sdc1 and sdc2) with parted to be used as backing devices, 
> 
> > /dev/sdc2 attaches fine
> 
> > problem with sdc1:
> 
> > # make-bcache -B /dev/sdc1
> > Device /dev/sdc1 already has a non-bcache superblock, remove it using wipefs
> > and wipefs -a
> 
> > # wipefs /dev/sdc1
> > wipefs: WARNING: /dev/sdc1: appears to contain 'dos' partition table
> 
> > # wipefs -a /dev/sdc1
> > wipefs: WARNING: /dev/sdc1: appears to contain 'dos' partition table
> 
> Did you try wipefs -a -f /dev/sdc1 ?

my wipefs does not have a -f option
 
> If that fails, just erase the first few MB of the device with zeroes:
> 
> dd if=/dev/zero of=/dev/sdc1 bs=1M count=10

I had tried this, but I see now that I copied from /dev/null instead of
/dev/zero and no data got copied :)

so, yes, your suggestion dd if=/dev/zero of=/dev/sdc1 bs=1M count=10 fixed it

thank you Pavel!

/Erik