On Fri, Jun 8, 2012 at 6:27 PM, Tony Harminc <[email protected]> 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 > http://www.youtube.com/watch?&v=1SCZzgfdTBo&t=211 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 [email protected] with the message: INFO IBM-MAIN
