Date: Thu, 12 Jun 2008 09:25:31 +0200 From: "DA Forsyth" <iwrtech@iwr.ru.ac.za> To: freebsd-questions@freebsd.org Subject: Re: xRAID disks.... Message-ID: <4850EB8B.12487.4CC2C0F4@iwrtech.iwr.ru.ac.za> In-Reply-To: <20080610145926.GA66984@owl.midgard.homeip.net> References: <484EACEB.7169.43FE1258@iwrtech.iwr.ru.ac.za>, <20080610145926.GA66984@owl.midgard.homeip.net>
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On 10 Jun 2008 , Erik Trulsson entreated about
"Re: xRAID disks....":
> > I suspect the raidinfo is stored on the disk somewhere and a suitable
> > 'dd' command can erase it. but where and how?
>
> That kind of information is usually stored last on the disk (where it is
> least likely to be overwritten by filesystems, partitioning info, or boot
> loaders), so if you overwrite the last couple of KBs on those disks you will
> probably be fine.
> (If you want to be certain you can always use 'dd' to nuke all the
> information on the disk. That will take longer time, but you get the extra
> advantage of testing all the blocks on the disk so that they work
> correctly.)
>
> For the first you could do something like:
> dd if=/dev/zero of=/dev/ad1 bs=1m skip=76318
> which should overwrite the last MB of ad1 with zeros.
I tried to overwrite just the last sector, but though dd reported
success (and took ages, seems it has to do a read for every skipped
sector) the data was still there when I used dd to display it.
I have just done a search for sector editing software but I cannot
find anything in ports. Starting to think of writing some C... how
hard can it be just to seek to a given sector and scribble zeros on
it?
so then I did this (overwrite last megabyte)and that did in fact zero
the last megabyte, taking away the raid info AND all the partition
info. not exactly what I wanted but I was going to repartition
anyway.
but I now have another disk with data and raid info on it and will
need a way to nondestructively remove the raid info there.
I did try the suggestion of 'atacontrol' but it did nothing, I also
tried 'gmirror clear' but that gives an error message, maybe I should
first create a gmirror then clear it. or maybe try the 'forget'
command....
hmmm, thinking now the gmirror create/remove route will probably
work. let me try it on a blankish disk and see....
--
DA Fo rsyth Network Supervisor
Principal Technical Officer -- Institute for Water Research
http://www.ru.ac.za/institutes/iwr/
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