Shmuel,
I guess this quote may be incorrect then: >From http://cmrr.ucsd.edu/people/Hughes/DataSanitizationTutorial.pdf "Secure erase does a single on-track erasure of the data on the disk drive. The U.S. National Security Agency published an Information Assurance Approval of single pass overwrite, after technical testing at CMRR showed that multiple on-track overwrite passes gave no additional erasure." I was referring to recent FBA drives, and was not referring to the CKD erase track. When I said overwrite I had no other meaning intended. I think sledgehammers work on any disk drive technologyJ One thing that is very different about current drive technology compared to SLED is that the concept of a cylinder is dead. It is faster for the servo to move the disk head from track to track across the platter rather then head switch down the cylinder, so recording is done in a serpentine fashion across the platter, then switching to the next head and back- hitching the arm at a point where the track switch is equivalent to the seek time. This means a greater settling frequency per physical track destaged. Unlike a SLED where the head stands still for 15 tracks of writes, current day disks will seek and settle the heads for every track. I do realize that the track capacity is much greater on current FBA than SLED, but the destaging objective of any scatter/gather buffer mechanism is to destage as much data in a single write as possible. Hence the average size of a destage operation is often, but not always greater than we observed on SLED. Finally, I don't know if simply not creative enough with my google arguments, but I cannot find that "NSA claims that it can recover data from residual magnetic fields" anywhere. Lots of probably, perhaps, and maybe, but conclusive claim from the NSA. Of course, I'd expect any claim to refer to current FBA drives and not a RAMAC I. I wonder if the NSA have managed to retrieve Nixon's missing 18.5 minutes of blank tape? Ron > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of > Shmuel Metz (Seymour J.) > Sent: Wednesday, February 22, 2012 10:17 AM > To: [email protected] > Subject: Re: [IBM-MAIN] Erasing data on disk volumes (2105-F20) > > In <002f01ccf108$587ad8a0$097089e0$@net>, on 02/21/2012 > at 06:18 PM, Ron Hawkins < <mailto:[email protected]> [email protected]> said: > > >You oversimplify the argument. > > As do you. > > >If you overwrite the data once, with anything, it is gone. > > 1. NSA claims that it can recover data from residual magnetic > fields; I have no way of cerifying that, but they have more > experise than either of us. > > 2. While on old DASD Write CKD actually erases data, that need not > be true on newer DASD. Was your statement specific to the 2105 > or intended to be general? > > -- > Shmuel (Seymour J.) Metz, SysProg and JOAT > ISO position; see < <http://patriot.net/~shmuel/resume/brief.html> http://patriot.net/~shmuel/resume/brief.html> > We don't care. We don't have to care, we're Congress. > (S877: The Shut up and Eat Your spam act of 2003) > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, send email to > <mailto:[email protected]> [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
