That would be RAID 3.

Parity and striping and compression are like shredding documents. It makes it 
hard to assemble and read the whole page, but there are substantial chunks of 
data in the clear tha may serendipitously contain a few credit card numbers and 
the zip code in the clear. That's enough to rip off a lot of petrol.


From: zMan <>
Sent: Fri, June 8, 2012 8:37:16 PM
Subject: Re: [IBM-MAIN] Failed Disk Data Exposure

On Fri, Jun 8, 2012 at 6:27 PM, Tony Harminc <> wrote:

> I was asked a couple of years ago to help recover some data from a
> failed system -- failed as in unnoticed single drive failure followed
> by second drive failure and discovery that backups had not been
> performed correctly. :-(
> I spent quite some time browsing recovered data in an image file. So
> much of the text data was either immediately readable, or trivially
> decodable, that I didn't initially realize that what I was looking at
> was an image of a single drive from a failed RAID 5 array!
> RAID 5 and friends have a lot of XOR'd data, and it all depends what
> it's been XOR'd with. For example, XORing EBCDIC letters with EBCDIC
> blanks generally just changes the case, which usually leaves the
> meaning pretty clear. Certainly some data will be gone, but much data,
> and many text strings in particular will survive.
> I just sent a very dead SATA RAID drive from home off for warranty
> replacement, and I would have erased or damaged it if it wouldn't void
> the warranty. So for me avoiding the $100 or so replacement cost is
> worth the small risk of them being interested enough in my data to
> spend time recovering it. But I can't think there is a business case
> for any large company not to be shredding failed drives when they cost
> only a few hundred dollars a pop. Google has a video of what they do
> to theirs

Wow. That's...scary! Who'd'a thunk. I thought striping was on a bit level,
and didn't think (and still don't understand why) there would be any
XORing. Tells you what I know!
zMan -- "I've got a mainframe and I'm not afraid to use it"

For IBM-MAIN subscribe / signoff / archive access instructions,
send email to with the message: INFO IBM-MAIN

For IBM-MAIN subscribe / signoff / archive access instructions,
send email to with the message: INFO IBM-MAIN

Reply via email to