Date:	Thu, 13 Dec 2007 17:27:39 -0500
From:	Bill Davidsen <davidsen@....com>
To:	Tejun Heo <htejun@...il.com>
CC:	Jan Engelhardt <jengelh@...putergmbh.de>,
	Justin Piszcz <jpiszcz@...idpixels.com>,
	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
	linux-ide@...r.kernel.org, apiszcz@...arrain.com
Subject: Re: Kernel 2.6.23.9 / P35 Chipset + WD 750GB Drives (reset port)

Tejun Heo wrote:
> Bill Davidsen wrote:
>   
>> Jan Engelhardt wrote:
>>     
>>> On Dec 1 2007 06:26, Justin Piszcz wrote:
>>>       
>>>> I ran the following:
>>>>
>>>> dd if=/dev/zero of=/dev/sdc
>>>> dd if=/dev/zero of=/dev/sdd
>>>> dd if=/dev/zero of=/dev/sde
>>>>
>>>> (as it is always a very good idea to do this with any new disk)
>>>>         
>>> Why would you care about what's on the disk? fdisk, mkfs and
>>> the day-to-day operation will overwrite it _anyway_.
>>>
>>> (If you think the disk is not empty, you should look at it
>>> and copy off all usable warez beforehand :-)
>>>
>>>       
>> Do you not test your drive for minimum functionality before using them?
>>     
>
> I personally don't.
>
>   
>> Also, if you have the tools to check for relocated sectors before and
>> after doing this, that's a good idea as well. S.M.A.R.T is your friend.
>> And when writing /dev/zero to a drive, if it craps out you have less
>> emotional attachment to the data.
>>     
>
> Writing all zero isn't too useful tho.  Drive failing reallocation on
> write is catastrophic failure.  It means that the drive wanna relocate
> but can't because it used up all its extra space which usually indicates
> something else is seriously wrong with the drive.  The drive will have
> to go to the trash can.  This is all serious and bad but the catch is
> that in such cases the problem usually stands like a sore thumb so
> either vendor doesn't ship such drive or you'll find the failure very
> early.  I personally haven't seen any such failure yet.  Maybe I'm lucky.
>   

The problem is usually not with what the vendor ships, but what the 
carrier delivers. Bad handling does happen, "drop ship" can have several 
meanings, and I have received shipments with the "G sensor" in the case 
triggered. Zero is a handy source of data, but the important thing is to 
look at the relocated sector count before and after the write. If there 
are a lot of bad sectors initially, the drive is probably a poor choice 
for anything critical.
> Most data loss occurs when the drive fails to read what it thought it
> wrote successfully and the opposite - reading and dumping the whole disk
> to /dev/null periodically is probably much better than writing zeros as
> it allows the drive to find out deteriorating sector early while it's
> still readable and relocate.  But then again I think it's an overkill.
>
> Writing zeros to sectors is more useful as cure rather than prevention.
>  If your drive fails to read a sector, write whatever value to the
> sector.  The drive will forget about the data on the damaged sector and
> reallocate and write new data to it.  Of course, you lose data which was
> originally on the sector.
>
> I personally think it's enough to just throw in an extra disk and make
> it RAID0 or 5 and rebuild the array if read fails on one of the disks.
> If write fails or read fail continues, replace the disk.  Of course, if
> you wanna be extra cautious, good for you.  :-)
>
>   
-- 
Bill Davidsen <davidsen@....com>
  "Woe unto the statesman who makes war without a reason that will still
  be valid when the war is over..." Otto von Bismark 


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