Re: cannot attach backing device, wipefs does not fix it

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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, 

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/dev/sdc2 attaches fine

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problem with sdc1:

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# make-bcache -B /dev/sdc1
Device /dev/sdc1 already has a non-bcache superblock, remove it using wipefs
and wipefs -a

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# wipefs /dev/sdc1
wipefs: WARNING: /dev/sdc1: appears to contain 'dos' partition table

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# 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