Re: Secure erase on an SSD MMA

Subject	Re: Secure erase on an SSD MMA
Newsgroups	comp.sys.mac.system
References	<6KqdnbEF3eda13HInZ2dnUU7-UmdnZ2d@giganews.com> <1mablsw.om0eeeovgdrcN%nmassello@yahoo.com> <ZpOdnTr0YeJk_HHInZ2dnUU7-T2dnZ2d@giganews.com> <55edcc97$0$9211$c3e8da3$5d8fb80f@news.astraweb.com>
From	Alan Browne <alan.browne@freelunchvideotron.ca>
Date	2015-09-07 14:00 -0400
Message-ID	<Q6KdnTHOIpRXTXDInZ2dnUU7-LednZ2d@giganews.com> (permalink)

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On 2015-09-07 13:42, JF Mezei wrote:
> On 15-09-06 11:55, Alan Browne wrote:
>
>> I used to simply write over entire drives with a simple and fast program
>> I wrote.  It's a little too case specific, but does the job.
>
> With TRIM enabled, one would think that initializing the drive with new
> file system would cause the OS to send TRIM commands for all blocks to
> mark them ready to be zapped.
>
> You could then fill the drive with one large file full of random data,
> and the SSD should then zap all blocks as it writes the random data to it.

> Something else to consider and it is likely impossible to really know.
>
> If writing a very large file results in the OS doing data writes of 4K
> (or multiples of 4K), the SSD no longer needs to do any safeguarding of
> partial pages since you are overwriting a whole page, and this greatly
> reduces write amplification and filling the disk would not preserve any
> of its data. (with or without TRIM).

My program writes 32K byte blocks.  The compiler may generate code that 
writes smaller blocks and/or the OS may break that down to smaller 
chunks before writing and the drive may break it down further.  IAC a 
smart SSD buffer algorithm should result in single physical block writes 
to the SSD even if the logical writes that hit that block occurred as 2 
separate events. (under and overlap).

I could also increase the block size significantly if I knew that would 
reduce the number of actual writes to a block.  But I believe the 
compiler may and the OS almost certainly uses smaller block sizes.

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Secure erase on an SSD MMA Alan Browne <alan.browne@freelunchvideotron.ca> - 2015-09-06 10:16 -0400
  Re: Secure erase on an SSD MMA nospam <nospam@nospam.invalid> - 2015-09-06 10:57 -0400
    Re: Secure erase on an SSD MMA Alan Browne <alan.browne@freelunchvideotron.ca> - 2015-09-06 11:16 -0400
      Re: Secure erase on an SSD MMA nospam <nospam@nospam.invalid> - 2015-09-06 12:32 -0400
        Re: Secure erase on an SSD MMA nmassello@yahoo.com (Neill Massello) - 2015-09-06 18:30 -0600
        Re: Secure erase on an SSD MMA Alan Browne <alan.browne@freelunchvideotron.ca> - 2015-09-07 09:56 -0400
          Re: Secure erase on an SSD MMA nospam <nospam@nospam.invalid> - 2015-09-07 11:30 -0400
            Re: Secure erase on an SSD MMA Alan Browne <alan.browne@freelunchvideotron.ca> - 2015-09-07 13:02 -0400
        Re: Secure erase on an SSD MMA JF Mezei <jfmezei.spamnot@vaxination.ca> - 2015-09-07 13:45 -0400
          Re: Secure erase on an SSD MMA nospam <nospam@nospam.invalid> - 2015-09-07 14:04 -0400
            Re: Secure erase on an SSD MMA JF Mezei <jfmezei.spamnot@vaxination.ca> - 2015-09-08 00:54 -0400
              Re: Secure erase on an SSD MMA nospam <nospam@nospam.invalid> - 2015-09-08 01:00 -0400
  Re: Secure erase on an SSD MMA nmassello@yahoo.com (Neill Massello) - 2015-09-06 09:36 -0600
    Re: Secure erase on an SSD MMA Alan Browne <alan.browne@freelunchvideotron.ca> - 2015-09-06 11:55 -0400
      Re: Secure erase on an SSD MMA JF Mezei <jfmezei.spamnot@vaxination.ca> - 2015-09-07 13:42 -0400
        Re: Secure erase on an SSD MMA Alan Browne <alan.browne@freelunchvideotron.ca> - 2015-09-07 14:00 -0400
  Re: Secure erase on an SSD MMA JF Mezei <jfmezei.spamnot@vaxination.ca> - 2015-09-07 13:35 -0400
    Re: Secure erase on an SSD MMA Alan Browne <alan.browne@freelunchvideotron.ca> - 2015-09-07 13:41 -0400
      Re: Secure erase on an SSD MMA nospam <nospam@nospam.invalid> - 2015-09-07 14:04 -0400
        Re: Secure erase on an SSD MMA Alan Browne <alan.browne@freelunchvideotron.ca> - 2015-09-07 14:10 -0400
          Re: Secure erase on an SSD MMA nospam <nospam@nospam.invalid> - 2015-09-07 14:12 -0400
            Re: Secure erase on an SSD MMA Alan Browne <alan.browne@freelunchvideotron.ca> - 2015-09-07 14:15 -0400
              Re: Secure erase on an SSD MMA JF Mezei <jfmezei.spamnot@vaxination.ca> - 2015-09-08 01:08 -0400
  Re: Secure erase on an SSD MMA John Albert <j.albert@snet.net> - 2015-09-08 23:05 -0400
    Re: Secure erase on an SSD MMA nospam <nospam@nospam.invalid> - 2015-09-08 23:13 -0400
      Re: Secure erase on an SSD MMA Alan Browne <alan.browne@freelunchvideotron.ca> - 2015-09-09 11:01 -0400
        Re: Secure erase on an SSD MMA nospam <nospam@nospam.invalid> - 2015-09-09 11:17 -0400
    Re: Secure erase on an SSD MMA JF Mezei <jfmezei.spamnot@vaxination.ca> - 2015-09-09 00:38 -0400
      Re: Secure erase on an SSD MMA Alan Browne <alan.browne@freelunchvideotron.ca> - 2015-09-09 11:04 -0400
        Re: Secure erase on an SSD MMA JF Mezei <jfmezei.spamnot@vaxination.ca> - 2015-09-09 11:41 -0400
          Re: Secure erase on an SSD MMA Alan Browne <alan.browne@freelunchvideotron.ca> - 2015-09-09 12:54 -0400

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